Sega fired the first shot, but the anti-Sega views were mostly taken up by Nintendo's fandom rather than the actual company. Didn't help much that Nintendo fans were all accused of being five-year-olds.
Mega Man has stretched itself so far that there's bound to be some of this. Among the main rivalries:
Classic timeline fans vs. the Mega Man Battle Network timeline. Though the latter is actually fairly faithful to the former in terms of themes, people who like the old-school, Nintendo Hard games see the Network timeline as an attempt to woo over fans of games like Pokémon and Yu-Gi-Oh!.
8-Bit Mega Man platformers vs. more-than-8-Bit Mega Man platformers. Some people feel the series declined after the NES era, with Mega Man 8 in particular being Snark Bait for its increased focus on new gameplay elements the core games never had. With Mega Man 9 and 10 not only becoming 8-Bit again, but also axing some of the moves Mega Man gained since Mega Man 2, a steady alternate backlash has arisen from people who think the series needs to be more progressive.
Speaking of Mega Man 2, there's an in-series rivalry between Mega Man 2 and Mega Man 3 fans. There's been a massive Broken Base over which game is superior, and it's not uncommon for flame wars to break out.
The video game example is Mario vs. Sonic. It was practically intended by Sega in the 16-bit era, since Sonic was created for the purpose of competing with Mario. It dissipated a bit once Sega quit consoles, but still exists because the rivalry become so deeply ingrained in video game history and bothfranchises are still very recognizable and popular headliners for their respective companies. Mario and Sonic at the Olympic Games and Sonic's appearance in later Super Smash Bros. games have taken advantage of this while burying the hatchet for the most part; the rivalry chiefly exists between older fans now (who also still argue over the aforementioned SNES vs Sega Genesis Console Wars). It's probably the closest thing to a video game equivalent of Coke vs Pepsi.
Mario Kart itself has a Fandom Rivalry between Mario Kart DS and other Mario Kart titles.
Within Sonic, you have "classic" (pre-Sega Dreamcast) fans vs. "modern" (post-Dreamcast) fans.
Within the Mario series, Koopalings fans and Bowser Jr. fans often positively hate each other. Many koopaling's fans often call Bowser Jr. a dull, boring Replacement Scrappy that stole the Koopaling's role as Bowser's offspring, while Bowser Jr. fans call the Koopalings shallow, overrated one note villains who have no characterization outside their appearance but still have an extremely grating Fan Dumb.
Thanks to Sonic & All-Stars Racing Transformed, many Sonic fans seem to have grown quite a hatred towards Vocaloid fans, particularly those of Hatsune Miku. The reason for this is because a survey was put up in the SEGA Forums over who people want as their next downloadable character. While the Sonic fans and other players of the game backed the likes of Billy Hatcher, Bayonetta, Toejam And Earl, and Ryo Hazuki, Miku received enough nominations to be put on the ballot, which caught the attention of the Vocaloid fandom. They voted en masse, and Miku ultimately placed 2nd, behind Ryo. The SEGA fans felt cheated that a character they largely have no interest in and were previously neutral to could now invade their game. (Regardless of the argument, she is the protagonist of the SEGA-produced Project Diva series.) The anime Hatedom jumped in, and debates about whether or not she's a SEGA character escalated into a Flame War within a week. It has gotten to where some people have announced they will become Griefers in an effort to drive Miku usage down. It should be mentioned that the Miku fans, who by and large do not play the game (until she gets in), are largely unaware of the hate going on on the other side.
On another note, fans of Sonic & All-Stars Racing Transformed has a pretty intense dislike for fans of the Mario Kart series due to its diametrically opposed approach to how items should function in a kart racer: Whereas Mario Kart has been item-centric since Mario Kart 64 with a stripped-down racing engine compared to other major racing franchises, Transformed is more of an arcade racer lightly peppered with items that are deliberately weak. This has split racing fans between those who like the more action-packed, chaotic progression of Mario Kart races that require on-the-spot thinking versus the calmer, more flowing races in Transformed that require planning ahead. (Most other kart racers have powerful items akin to Mario Kart, hence why such a rivalry never reached this intensity until now.) The Transformed fans accuse Mario Kart fans of being skill-less hacks who need luck to win a race, whereas the Mario Kart fans accuse Transformed fans of racing snobs who don't know how to deal with unexpected setbacks.
Within WoW, you have warriors-versus-paladins and more famously, warlocks-versus-mages (although most people in those debates see it as a friendly running gag to bash each other, especially since a lot of these guys probably have alts of the opposing classes.).
Within 'World of Warcraft', you also have Horde vs Alliance. A major source of contention that causes a broken base. That's right, just like the factions in game, the fandoms are at war with each other. While most players do have characters on both sides (like the class debates above) they all have one clear favorite, and there are many flame wars over which is better (from meta-game perspective all the way down to who has the better war machine in lore), which Blizzard favors in terms of buffs or for story focus, etc. Fans of lore also see a similar rivalry between people who prefer "war" between the two factions and a "peace" between the two factions.
EVE Online players tend to stay away from the fracas for some reason, oddly enough for an MMORPG that has been demonstrated to be Serious Business - probably due to a different gameplay emphasis.
Star Trek Online might be the first to start some friction, even though it seems like the two games will have absolutely nothing in common besides starship combat in space online, that never stopped anyone.
World of Warcraft versus Rift: Either Rift is a half-assed WoW knock-off that is on the verge of disappearing into obscurity...or it did WoW one better, and the only reason WoW still has fans is because some people have no taste. There's very little middle ground.
If you can find a discussion on SW:TOR's main forums that involves Guild Wars, you will find someone lying about Guild Wars 2 just to make it look bad. There was one thread where a guy claimed he was playing the GW2 beta to reinforce his argument that he knew TOR was superior. The GW2 beta wasn't even out yet. Some GW2 fans love this and go troll the TOR forums, only making the problem worse.
In case you haven't noticed the trend by now, over 90% of the Fandom Rivalries in the MMORPG genre can be summed up as World of Warcraft vs. whatever game is currently in second place in popularity.
To a degree you also have World of Warcraft vs. the first three Warcraft games, due to the seeming abandonment of the original strategy format. Even proposed films have focused more on World of Warcraft than the original games.
Elite Beat Agents versus Osu! Tatakae! Ouendan, with OTO fans saying that EBA is a watered down version of Ouendan and EBA fans calling OTO fans "weeaboos" (never mind the fact that EBA had a manga artstyle too).
Due to both series' Mission Pack Sequels, Metallica vs. The Beatles is an easy way to start an argument between fans of not those two bands, but rather of said video game series. This despite the fact that both bands are completely different.
Guitar Hero and Rock Band vs. Bemani (particularly Guitar Freaks and drummania, the inspirations for GH and RB). The tension seems to have calmed down in recent years, although the introduction of Guitar Freaks XG (a successor to the 3-fret Guitar Freaks that adds two more fret buttons) re-ignited things a little bit.
Tekken vs. Dead or Alive. This one's particularly interesting in that one of the actual game designers, DOA creator Tomonobu Itagaki, actually promotes the rivalry (Itagaki has been very outspoken in criticizing Tekken), and that, starting with DOA3, the series became console-exclusive on Xbox/Xbox360, while Tekken, although multiplatform, is still considered by fans a PlayStation franchise. Basically, this is a fandom rivalry that involves both games and the systems they play on.
Super Smash Bros. vs. any fighting game. Due to its game mechanics, it's heavily debated whether Smash is more technical or less technical than other fighters; it may be considered less technical because the control scheme is comparably simple, and it may be considered more technical because the game is more about manual advanced technical maneuversnote For example, lag-canceling aerial attacks is manual in Smash. Traditional fights don't have any landing lag at all. psychological skill, matchup knowledge, and creative playstyle than simply health bar depletion and button combinations. On the other hand, Smash greatly decreases the focus on combos, and in Brawl they are nigh nonexistant, taking away a bit of depth. However, compared to other examples on this page "eh, apples and oranges" is a much more acceptable viewpoint.
Halo fans vs. Metroid Prime fans. Doesn't help that the resemblance is superficial at best and that both series actually do appeal to different tastes.
There's also a substantial rivalry between the Halo and Half-Life fandoms, possibly mirroring the Console vs PC conflict.
There's another rivalry which is much more vicious between fans of Halo and fans of Warhammer 40,000, specifically on the topic of SPARTANs vs. Space Marines.
This one is also related to the fact that both were incredibly influential First Person Shooters, and nobody can seem to decide which one was more important (Half-Life, because it's earlier? Halo, because it's more widely-known?)
Good god, Battlefield versus Call of Duty, a rivalry deliberately started by Electronic Arts themselves. The intense amount of Fan Dumb spouted by both sides is enough to give one a headache. Not completely unrelated to this is...
Steam versus EA's Origin. One of them is a well-established digital games platform (which Call of Duty games are directly integrated to, controversially starting with Modern Warfare 2). The latter is coming out with the explicit purpose of destroying the former. Compounded by EA refusing to comply with Steam's terms of agreement, which led to the removal of some games (Crysis 2 and Dragon Age II) from Steam, which will certainly end up on Origin when it comes out.
Don't believe us about the Battlefield vs. COD war? Go on ANY Youtube video about either game. Scroll down to the comments. If you are not frustrated, you deserve a medal.
And then came COD vs. The Elder Scrolls V: Skyrim vs. Halo vs. Battlefield. You know, since games of different genres should be compared to each other to reach a logical goal.
To a certain extent, there's even a Halo vs. Marathon rivalry, as some people think Bungie merely recycled the latter's ideas into the former with more modern production values and more commercial success. The Mac vs. Windows rivalry (as described elsewhere) might also have something to do with it, since the Marathon trilogy was originally released for the Mac before fans created the Aleph One cross-platform port, whereas Halo was originally made for Microsoft's Xbox (though it was later ported to the Mac as well as the PC). However, in this case, it's more acceptable and common to like both than usual.
Speaking of which, Marathon vs. Doom for old-school FPS supremacy. The former was considered technologically superior and had an infinitely deeper storyline, but since it was originally released for the Mac, which has never been known for its huge gaming community, the latter was much more widely played. And, of course, there were probably Doom players who just liked killing stuff without having to follow a story.
In all honesty, Call of Duty vs. EVERYTHING. Their Fan Dumb seems to almost take pride in bemoaning anything and everything that isn't Call of Duty, even itself, judging from their Fan Wank about most of the games being on Nintendo consoles. While software-hardware porting limitations give legitimate reasons to dislike the game, their Fan Dumb seems to criticize it for solely being on the Wii at all, with the best argument they can give being "OMFG GRAFFIX SUXORZ SO ITS GAY".
The Splatoon fandom has specifically positioned itself as the anti-Call of Duty community. Frequent talking points brought up by Splatoon fans are that Call of Duty has become too Strictly Formula, has a Real Is Brown aesthetic, and is full of the typical violence and deathmatches of the shooter genre, all in contrast to Splatoon.
Team Fortress Classic players vs. Team Fortress 2 players. The former people tend to fall into They Changed It, Now It Sucks, with the amount of features being unnecessary or ruining the gameplay and look down on the latter game as being too "noobish". It doesn't help that TF2 is much more well known than classic now. You know how this proceeds.
Team Fortress Classic/2 vs. Counter-Strike (Source). Both from Valve, both started as mods (though Team Fortress goes back even further as a mod for Quake), both with diametrically opposed styles of gameplay. Bound to be conflict? You bet.
Also nice to know that before Counter Strike, Team Fortress Classic was the most popular online shooter. Now it's usually back and forth between Counter Strike and Team fortress 2/Classic
How to make the Fans rage? Ask who would win in any forum that knows both franchises
Final Fantasy vs. Dragon Quest, although this one is probably a little stronger in Japan, since love for the Dragon Quest series elsewhere lies mostly with a cult following.
A stronger example for Americans would probably be, within the Final Fantasy series, pre-Final Fantasy VII games vs. FF7 and anything beyond. Final Fantasy VI and Final Fantasy VII in particular have fandoms with a hate-on for one another. The other strongest rivalries are FFVII vs. FFX, FFIX vs. Underappreciation, and FFVIII vs. every other game in the series.
There also seems to be one for FFV versus any of the more story driven ones.
This got really interesting after the companies that made the two series (Squaresoft for Final Fantasy, Enix for Dragon Quest) merged into the new company, Square Enix. You might think that this would make the rivalry less intense as both series are now made by the same company. There are some fans from each side who claim that entries of their series made since the merger have been lesser in quality due to being "tainted" by having employees who were originallly from the other company working on them.
A smaller scale rivalry is Final Fantasy vs. the Tales Series, or, to be more accurate, Final Fantasy VII vs. Tales of Symphonia. Both games are considered by and large to be the greatest games in their respective series, and thus are at the heart and passion of next to all of the flame wars of these two franchises.
Metal Gear fans think Splinter Cell fans are boring, wish-fulfilment-craving thirteen-year-old boys who like to look ultra-serious all the time, have no sense of humour, and aren't smart enough to understand a complex, involved and challenging story. Splinter Cell fans think Metal Gear fans are moronic, hyperactive children who wouldn't know true stealth if it crept up behind them and snapped their necks, and aren't mature enough to care about the story of a game that isn't from Japan and doesn't have a vampire in it. Thief fans tend to dislike both camps for being too stupid to understand a story which isn't spoonfed. It's kind of hilarious watching them all go at it.
The Metal Gear Wiki has a neutral article on Splinter Cell. The Trivia section for the game (which no longer exist) once mentioned that the fans of one series often dislike the other, concluding with, "It's a good idea to ignore both of them."
The best part is that Konami and Ubisoft see it in a more friendly light. Both even cooperating to allow each other to create cameos in their games. Cameos that don't involve any shots at each other even.
Heroes of Newerth and League of Legends are both inspired by the original Defense Of The Ancients All Stars mod - the former is a straight copy, the latter has a few superficial differences. Yet if you listen to their respective fans on the forums, LoL is ridiculously easy to master and only for kids, is too different, the items are boring and the graphics suck; and HoN has a terrible user interface, unintuitive gameplay, is not different enough, the items are boring and the graphics suck. Arguments like 'the automap is on the wrong side of the screen' and 'the item icons are ugly' are not uncommon. Very little effort is spent explaining the reasons why their favourite game is good as opposed to why the other game is trash.
With more MOBAs, like DOTA 2, coming out soon, this rivalry is starting to shift to the new contenders as well.
Indeed, while LoL and HoN might previously have been the heavy hitters in this rivalry, it might be more accurately summarized now as "fans of any MOBA vs. fans of every other MOBA".
A very old one that still persists among the retro community: Repton versus Boulder Dash. Made worse by the fact that they have completely different styles yet appear very similar on the surface, to the extent that non-fans often mistake them for clones.
The Fate/stay night war between the Unlimited Blade Works and Heaven's Feel scenarios still hasn't boiled down. Whether it's a battle between the heroines: Rin is a strong, hardworking, independent woman vs. Rin is a cookie-cutter Tsundere; Sakura is a sympathetic, kind-hearted Woobie vs. Sakura is a boring Nice GirlFirst Girl Wins. Shirou's ideals: It's impossible to save everyone, but it's beautiful to try anyways vs. ultra-dense Lawful Stupidmoralfag; It's better to realistically look at the world vs. moral relativism is for senseless 80s Anti-Heroes. The quality of the narrative: An epic and hopeless supernatural brawl vs. standard Shounen plot line; A look at the darker aspects of the Grail War vs. two weeks of people dying and badly written sex scenes. What's worse is that any argument among Type Lunatics tends to curve right back to where it began, resulting in an endless loop of "debate".
Though it's more of a Broken Base, Atlus fans can't seem to agree on whether the classic Shin Megami Tensei games or the newer games (Such as Persona 3 and Persona 4) are better. Or whether Persona 3 or Persona 4 in general were better.
There is also the matter of general SMT fans shying away from the P3&4 fandoms due to their ignorance of other sub-series in the franchise. On the opposite side, there are people complaining that Shin Megami Tensei IV is not Persona 5.
For that matter, there's also a bit of heat between fans of Shin Megami Tensei and the Pokémon series, the debates usually ranging to accusing one side of either being too dark, or too soft. The both of them being well-selling, long-lasting Mons series, and having an undying love for spin-offs doesn't help any.
Perhaps one of the reasons is that it's not uncommon to move from RuneScape to Artix Entertainment (being that both games are free-to-play Role Playing Games with a bit of comedy involved, and the resemblances are even closer with AdventureQuest Worlds now in place), and thus the old animosity that the old RS fans have carry over to AE.
Jak fans and Ratchet & Clank fans absolutely despise each other, claiming one game ripped off of the other, despite the developers being good friends and business partners.
The fact that the characters starred in a game together shows how nonsensical this hatred really is.
And in another game together as well, although they appear as rivals. Still, once again they're in the same game.
People who buy video games look down on pirates because their piracy leads to draconian forms of Copy Protection that end up doing nothing to the pirates and only hurt the paying customers (and in some cases lead to games being cancelled completely). Pirates look down on the paying customers and think they are all complete idiots because they paid for something they could get for free.
Another argument pirates often use is that paying for games despite said Copy Protection causes companies to feel like they can get away with anything.
Dark Souls vs. The Elder Scrolls V: Skyrim are both high-fantasy RPGs that came out around the same time. The debate usually boils down to JRPGS vs. WRPGS (despite Dark Souls being styled much like a WRPG) and old school challenge vs. open world fun.
Touhou fandom gets some hate from the more general Shoot 'em Up fandom for not focusing on the games, and the games themselves being mechanically simplistic. When the Touhou fans actually notice, they generally respond that the other games have boring, ugly patterns and mediocre writing.
Touhou fans have a rivalry with other similar games over the matter of which is better (and the fact that most are trying to Follow the Leader.)
There's also a rivalry between them and Kantai Collection over the matter of general popularity and the fact that various Touhou fan artists have instead switched to doing art of the latter series, irritating the former's fans. Touhou fans are fond of calling the girls in that barely characterized while Kantai fans are fond of saying Touhou is Not So Different.
Within the general shmup fandom, fans of "old-school" shooters vs. fans of Bullet Hell shooters and modern shooters in general, particularly those by CAVE. The former hate newer shmups for featuring girly-girl ships and characters instead of the more military- and scifi-themed visuals of older games and dismiss their high bullet counts as cutting corners. Meanwhile, danmaku fans scoff at more classical shooters for having drab visuals and being too boring to play because they don't have enough bullets on-screen.
Also, CAVE vs. 8ing/Raizing. It should be noted this isn't much of a rivalry as CAVE out lasted the latter and some of the latter's staff joined CAVE afterwards, resulting in games like Ibara
Left 4 Dead fans VS Left 4 Dead 2 fans. On the camp of game 1, people will claim that the game has a darker feel, better characters, less bugs, and doesn't have the silly amount of guns or melee weapons or new special infected that the sequel has. On the camp of game 2, people will tout that the sequel is better due to having more variety in guns and zombies, better designed levels, and more game modes to play in. Any mention over which games is better or just mentioning the infamous Left 4 Dead 2 boycott will bring both camps together armed with flaming pitchforks.
Half-Life fans vs. Portal fans. This is an Enforced Trope: to make sure Portal doesn't get a hatedom, Valve set it in the Half-Life universe, and Aperture Science (the facility in Portal) became rivals of Black Mesa (the facility in Half-Life). In addition, Half-Life 2: Episode Two featured a discovery of an Aperture research vessel, Borealis, with Eli Vance vowing to destroy it "whatever it takes", and in Portal 2 Cave Johnson implies Black Mesa stole Aperture Science's corporate secrets and made profit of them themselves. While some fan circles do seem to get in an argument whetter Aperture Science or Black Mesa is "better", most of them became fans of both, destroying the trope.
Dragon Age: Origins and The Witcher. Both are very competently made western RPGS, both have Darker and Edgier settings, and both explore a variety of mature themes, such as loyalty, racism, sides in conflict, and complex morals. The Witcher fans argue for the game's more interesting setting, well-written story and beautiful graphics, while Dragon Age fans argue for the game's fast-paced tactical combat, more approachable and likeable characters and more polished look and feel.
This escalated during the long wait for both series' third installment, particularly after E3 2014, both showed gameplay, but Bioware went on to reveal characters while CDPR did interviews. What happened was Bioware revealed several romances of which two were homosexual, while CDPR went on to discuss sex in games and marketing. Due to the gaming media running wild with OM Gz homesexul carectahs, Witcher fans accused Bioware of being pointlessly and aggressively PC and using sex for marketing. Bioware fans argued back that Bioware has been about romance, and the Witcher 2 had a playboy article for it's marketing and has always been overtly sexual.
Games rewarding T-Spins on versus, most notably Tetris DS, have been very polarizing for straying away from the original Tetris formula and de-emphasizing Tetrises. Nonetheless, there are players who enjoy playing games with T-Spins competitively.
GOD HELPS YOU IF YOU'RE TALKING ABOUT THIS WITH BRAZILIANS!note Soccer is one of the most famous sports in Brazil and because of that, the Rivalry is even bigger there.
Minecraft and Terraria fans shifts between this and Vitriolic Best Buds. Minecraft fans have accused Terraria of being a ripoff of Minecraft, but in 2D, while Terraria fans have accused Minecraft of copying from Terraria after its release with Minecraft's subsequent addition of bosses and character development. Luckily, this war between MC and TA ended long ago with the mojang crew recommending people to also play Terraria, allowing the fandom to shift its rage towards Fortresscraft and similar games instead. It also didn't help the rivalry that, aside from a block based world, the two didn't really have anything that wasn't inherent in the blocks system in common, with Minecraft being a 3D building sim, but Terraria being a callback to old platformers and metroidvanias.
Roblox. people on Roblox forums get banned easily when they say that MC is better, or sometimes even when they just say the word Minecraft. They briefly teamed up to take down SOPA, however.
Diablo III vs. Torchlight II, the long-awaited sequel to a classic franchise and the sequel to the Spiritual Successor to that same franchise created in the interim, both released in the same year. While many fans on either side will recognize the merits of the other, they're just different enough that it's hard for anyone to enjoy both.
Initial D Arcade Stage vs. Wangan Midnight Maximum Tune. Both are arcade racers based on manga franchises that cover the topic of illegal street racing, so it's easy to see where that one's coming from.
And, in The Nineties, Ridge Racer vs. Daytona USA. The series's fans used to not get along at all, but the appearance of Daytona's Hornet in the PS Vita release of Ridge Racer seems to have toned down the feud.
Some people despise linearity in games, and only play Wide Open Sandboxes, while looking down on anyone playing anything even remotely linear as a child who needs their hand held the whole time so that he doesn't get lost. And the other side argues Sandbox games give the player too much freedom to the point of being confusing, while also making it more difficult to tell a coherent story. Overlaps with Americans Hate Tingle and Germans Love David Hasselhoff, as Japan tends to preffer linearity while Westerners preffer openness.
It's rare but the opposition would accuse sandbox fans of the same thing since sandbox games can be played "without any real consequences" since dying doesn't actually mean much.
Fans of Take Two's NFL 2K series have had it in for Madden NFL ever since EA purchased the exclusive NFL license and drove the former franchise off the market.
Freespace fans vs Wing Commander fans, although both fandoms treat it as more of a friendly rivalry anymore (that there is a major Wing Commander mod for Freespace is telling). Freespace fans and Battlecruiser 3000 AD fans had a more bitter enmity, mainly due to an incident where Battlecruiser's creator made a bid for buying Freespace's license, and the resulting Flame War.
And you can toss fans of the Video Game/Xwing series in for good measure. The fan rivalry between Wing Commander and X-wing especially got quite heated.
Fans of Pokémon vs. fans of Spectrobes for DS Role Playing Games. Both Spectrobes and Pokémon Diamond and Pearl came out around the same time, inciting massive arguments about which one has better gameplay, graphics, and story.
Most users on Steam's Team Fortress 2 forums hate anything Mario or Sonic. Just the mere mentioning of them will cause users to go into a frenzy. YouTube and deviantART TF2 fans don't mind Mario or Sonic, though.
Rather odd as the users of the Workshop show heavy support for having the Mario-expy hat in the game.
Much like the Spyro the Dragon example above, Crash Bandicoot has rivalries between people who accept all of the games, people who like everything up until the Radical Entertainment games, people who hate anything post-Naughty Dog, and people who like the Radical games but don't like the rest.
Dungeons & Dragons Online deserves a mention for its fanbase's inter-medium rivalry with that of pen-and-paper Dungeons & Dragons. The reasons for the dispute are varied and the disdain is not universal (some people enjoy both), but common criticisms include the game not emulating the experience of a D&D campaign well enough, being too derivative of World of Warcraft/other MMO's in general, having too much pay-to-unlock contentnote most of which can be unlocked in-game on a per server basis free of charge, but that rarely factors in., and so on.
Zynga vs Kabam on Facebook. Especially with players of games like Kabam's Kingdoms of Camelot who look down on FarmVille and its siblings. "If you don't want to get attacked,go play FarmVille."
BlazBlue: Calamity Trigger originally had a short-lived rivalry with Street Fighter IV, but interestingly, this has been overshadowed by another rivalry with Guilty Gear. The reason this is strange is that both games are made by the same company, Arc System Works, and are extremely similar; both have labyrinthine plots, both feature fast-paced combat, both have wacky characters, both have AnimesqueMagitek settings, and both have amazing heavy rock/metal soundtracks. What's worse, Arc Sys only recently got back the creative rights to Guilty Gear, and only has the productive capacity to work on one franchise, making the two games in direct competition.
The main reason the two are in rivalry with each other is the differences in mechanics. Some feel Guilty Gear had a better fighting system due to its technicalities and depth and felt that BlazBlue dumbed it down too much, while others feel that Guilty Gear is too difficult to get into and feel that BlazBlue's accessibility makes it a better game. There are other things such as the guard primer system, the way barriers work, floatiness, and other mechanics that Guilty Gear fans didn't like in BlazBlue, but that would require an essay to get into detail. Fortunately, it appears Arc System Works has become quite Genre Savvy about this, as for the new entry in the series, BlazBlue: Chrono Phantasma, they've attempted to blend the good aspects of both games together in an attempt to win over the alienated Guilty Gear fans and keep the current BlazBlue fanbase.
The NetHack and Angband fandoms gripe over the cryptic gameplay and inside jokes of the former, and over the slow pace and grindiness of the latter. There's also a myriad of variants of both roguelikes, and some of these variants have quite the vocal following...
The rivalry between Dwarf Fortressfortress mode and adventurer mode is milder than it used to be; most players with a preference still find something to like about the other mode. It will become apparent when discussing one mode and including information that could only be gained from the other mode.
All of the Xeno games have a sizable hatedom from the other 2 Xeno series. Xenogears fans dislike Xenosaga because it wasn't a full-fledged prequel and more of a reimagining of the Gears universe at best. Both Xenogears and Saga fans dislike Xenoblade because it has little in common with the other Xenos and the plot and characters supposedly not being up to the standards set by the previous Xeno games. Xenoblade fans dislike Xenosaga due to being a "space soap opera" and its plot being a mess. Even Xenogears gets a bit of hate for its second disc, and almost all Xeno fans from all three series hate Xenosaga Episode 2 for its battle system.
Retro Studios deciding to make Donkey Kong Country: Tropical Freeze instead of a fourth Metroid Prime game reignited the long-dormant Metroid / Donkey Kong Country rivalry. To elaborate: Super Metroid came out in 1994 and received tremendous acclaim from players and critics alike until Donkey Kong Country stole its thunder later that same year. Today, both games are considered classics, but at the time, angry Metroid fans criticized DKC, claiming it relied too heavily on good graphics and sound but lacked any real depth as a game. Metroid Prime fans seem to think that Retro is the only studio qualified to make a good modern Metroid game (after their disappointment in the Team Ninja-developed Metroid: Other M) and that Donkey Kong Country should be developed in-house by Nintendo (or not at all, according to some of the Hate Dumb) so it doesn't take up their time. Similarly, DKC fans think Retro is the perfect studio to take up Rare's mantle (after their disappointment in Donkey Kong Jungle Beat, the Country series' total absence from 1996-2010, and the critical and financial success of the Retro-developed Donkey Kong Country Returns), but the more overzealous among them tend to stereotype Metroid fans as entitled crybabies and love to point out that DKC is typically a much higher-selling series than Metroid.
Then, you have Federation players vs. Klingon Defense Force players vs Romulan Republic players. KDF and Rom players hate the Federation as they're usually seen as a Creator's Pet, Fed and KDF hate the Romulan Republic due to their overpowered ships and Fed players hate the KDF and Romulan Republic as they get ships that cloak and they don't.
Then, you have rivalries between message boards, particularly the official, Perfect World-hosted one and the official Reddit-hosted one. The PW one is looked down upon by the Reddit posters because it's devolved into a pit of wank, complaints and just outright negativity. The PW posters looks down on the Reddit one because they believe that they're nothing more than Cryptic dev buttkissers who allow the game to continue to "deviate" from the "true Star Trek game it could be"