The Devil May Cry series became prey to this, with hard-core fans for the older games ripping on DmC, and the other camp in favor of it. There will be blood.
The fanbase for Super Smash Bros. was split into two camps following the release of Brawl, the third entry in the series which did away with advanced techniques that helped Melee build up a competitive scene in its early years all because the creator of the series, Masahiro Sakurai for whatever asinine reason didn't like the fact a competitive community had even sprouted up from what was intended to be a free for all party game where anyone can win thus why he made Brawl the way he did to discourage advanced play. Notably, he added a mechanic that even most casuals didn't like, known as "tripping," in which your character would randomly fall flat on their ass when running. Because of this, many fans who loved the last game tried to like Brawl, but quickly found themselves sticking to the game that actually had competitive value. However, some people liked Brawl's slower more casual friendly pace (not to mention Brawl ironically had some competitive value in the end; it was just more defensive/campy based which irked many people who prefer the offensive options and overall speed and fluidity of Melee) and that was all it took to cause hundreds upon hundreds of debates that quickly turned into raging infernos of a flame war as people from both the Melee and Brawl fanbase bashed on each other's preferences and rather than try to respectfully debate the merits of both games quickly resorted to ad homeinems (calling each other stupid in other words)
If that wasn't crazy enough, people strictly in the Brawl community got into flame wars over a certain character known as Meta Knight from the Kirby franchise, who lots of people saw as extremely cheap and even broken when compared to most of the cast who suffer from being in a very unbalanced roster. Some argued that Meta Knight isn't that hard to beat in competitive play as some characters do stand a chance against him. Others feel that it's irrelevant as half the cast is complete crap anyway no thanks to how slow and laggy the game is. While the mysterious swordsman was in fact banned from competitive play for a while, it was eventually decided to leave it up to tournament organizers whether or not to ban him from a tournament. This caused people who liked the fact the most OP character in Brawl got justly banned for a while to flip out completely and go berserk on the forums leading to more flamewars concerning Meta Knight's legality.
As if it was even warranted to begin with, some unsavory fans have rudely bashed 4 for so much as looking like Brawl in terms of gameplay footage. The flame wars reached a zenith when people got to try out the demo for Smash 4 on both Wii U and 3DS and again, some unsavory fans trashed 4 for feeling like Brawl despite the fact that A. its a demo and physics, lag, etc. are generally expected to be fine tuned to perfection by the time of the final product and B. many who didn't care for Brawl's anti-competitive slow gameplay like how 4 feels faster and even more fluid, yet not on Melees lightning fast speed. Even some professional players haved noted that 4 feels like its got more competitive viability than Brawl did.
Another sensitive issue is whether or not a few people pirating games really hurt game developers. Topics also somehow get morals involved.
DRM is the new big one, unique in that there are very few people actually supporting it, yet the Angry Internet Men somehow manage to start a flame war anyway.
Almost anything involving Final Fantasy, such as which one sucked, which one was awesome, whether they're the best thing since sliced bread or the sign of everything wrong with the game industry today.
Calling any Final Fantasy character emo, but especially protagonists like Cloud and Squall, is asking to be burnt to ashes, just to be put back together so you can be burnt down again and again.
Kefka vs. Sephiroth.
Aeris vs. Tifa. Or, if you're really looking for a fight, try asking any fan whether Cleris, Cloti or Zerith are the OTP.
This cannot be stated enough how MUCH of a flame war the Love Triangle Debate for FF7 can get out of hand. Most Final Fantasy forums have a stickied thread dedicated to it, just to spare other members the drama. These threads often exceed the hundred-page-mark.
Then there's the matter of whether a character's name is/should be romanized "Aeris" or "Aerith". The latter was the original intent, but a lot of people prefer the former and will go out of their way to defend it.
Team Fortress 2 is one of the most popular team-based online shooters ever. Beyond this, there is no aspect of the game that is not subject to actinic flamewars. There is no action Valve can take that will not spark flames on the forums. This war will end when the world ends and/or the last copy is deleted.
Who would have thought hats could spark that much controversy?
The Mannconomy Update (trading, item set advantages and the ability to buy items (you can still get them free)) can be thought of as Valve pouring a tank full of gasoline out and waiting for the community to blunder in with a lit match.
Try to do a comparison of the same game across multiple platforms without people tearing each other apart over which is the best version.
And it all comes crashing down when fans of Persona 2 or, better yet, more traditional Shin Megami Tensei games enter the fray. Like Fallout, you are not allowed to like them all.
One of the more famous subjects for a flame war is: "Which is better, Halo or Call of Duty?"
While on the subject of Halo, go to it's official website, which, with all the flames on its forums, could also be known as hell. You're guaranteed to see multiple threads decrying any newly revealed feature for the next game, declaring the "death of Halo", and demanding that the studio apologize for the failure that was the last critically and commercially successful game. Inside these threads, wars between the "I liked that game" and "This new feature sounds fun" guys and the "Nope, the whole series is ruined" and "Halo is Call of Duty now, my life is over" guys will rage until the last Halo game is released. And probably after that.
Speaking of Runescape, what about their sister site, Funorb?! Funorb is practically dead, and it's festering with people who refuse to let go of the site and flame on the forums that they want something done.
Left 4 Dead starts one whenever anyone dares to compare the first game to Left 4 Dead 2. Bring the marshmallows if you attempt to bring up the boycotters of the sequel and bring a flame retardant suit if you ever mention the balance of VS mode.
Please... consider the consequences before asking, "Does Heavy Rain qualify as a video game?"
In recent months, this has expanded into a general debate. Is X a video game? For a given value of X, every title from Heavy Rain to Journey to The Last of Us(!) has been put on the slab to serve as the sacrifice du jour to the gods of this particular flame war.
Modern Warfare is particularly infamous for garnering a large hatedom attributed to some design decisions of Modern Warfare 2 and the Infinity Ward CEO sacking fiasco afterwards, to a degree that it fostered Metacritic bombings and a very vocal flame war on both sides, particularly since the Call of Duty franchise is now one of the biggest-selling out there. Those arguments also extend to modern shooters in general.
A war within the Nintendo fandom has brewed since 2010 due to the influence of Sean Malstrom. On one side stand the "Orthodox" Nintendo fans, who just enjoy the games for what they are and tend to like whatever Nintendo gives them, on the other are the Malstromites, who tend to like only the Nintendo games that adhere to the Blue Ocean strategy. Things get heated in that the Malstromites tend to view those Nintendo games that do not adhere to the strategy as being actively destructive for Nintendo, and thus begin to flame games like Super Mario Galaxy 2, The Legend of Zelda: Spirit Tracks, or Metroid: Other M, or even call for the firing of Satoru Iwata, Yoshio Sakamoto, and Shigeru Miyamoto, much to the dismay of Orthodox fans.
Mass Effect 2 has become this ever since a series of reviews were made popular, both of which tore into the main plot, highlighting what they perceived as faults. BioWare's forum has been lit up with crusader-esque assaults from both sides while constructive criticism is lost in a slew of ranting.
Do NOT mention Player VersusPlayer on the City of Heroes forum, nor should you take a side in the "The writing is good/the writing sucks" debate without first donning a helmet.
The very bitter contentious arguments over the hardware specs of the Wii U, and whether or not it is "next-gen". Hoo boy!!, the arguments are so intense you would have thought someone denied/justified the Holocaust. Both sides are vocal, but dissenters are the most vitriolic. Probably doesn't help that game developers give conflicting opinions about the system and it's capabilities. Either way the passion is dumbfounding.
WRPGS vs.JRPGS , dear God you can't even mention WRPGS and JRPGS in the same sentence withourt starting a huge flame war on most gaming forums.
The League of Legends community forums, over just about anything from changes made to the game to what country should be allowed to even play on it.
There's an ongoing argument between Silent Hill fans over whether or not the games produced by Team Silent are better than those produced by Climax, whether the games from 4 onwards are more action orineted than their survival horror predecessors, and whether or not the second game is a Tough Act to Follow or extremely overrated.
In-universe example: the EVE Online in-character forum features in-character flame wars. The most prominent are those between the Amarr and Minmatar roleplayers, with an effect similar to what would happen if US Marines and Taliban fighters were to be sharing an internet forum.
Related to the above Nintendo example ANYTHING Nintendo related as a company, starting with the Wii up to the Wii U. The flame wars are just super toxic, filled with nothing but Hatedom, Fandom, Hate Dumb, Fan Dumb, and Broken Base over whether or not the Wii U is next gen or not, the lack of new IP's and what qualify as a new IP (Nintendo has made new IP's, but whether or not they're aesthetically appealing is a different can of worms), the lack of third party support as far back as N64 and whose to blame for this Nintendo or game developers for being lazy, the kiddie/family stigma, should Iwata be fired or is he being scapegoated? wash rinse and repeat with Reggie, and Myamoto, the lack of a robust online infrastructure vs that's not what Nintendo is about, etc etc etc.. Doesn't help that people accuse the gaming media as part of the problem. Flame wars are common in the gaming community yes, however Nintendo is completely different monster all together with a gazillion different shades of conflicts and issues by extension. For example casual gaming vs "core" gaming and the definition of those terms, motion controls vs standard controls, photo realistic graphics vs that's not what Nintendo is about. In fact arguably most major debates revolving around console gaming have Nintendo as the root of the argument...or it eventually leads to Nintendo. Sony, and Microsoft wars are nowhere near as bad as the Nintendo debates.
On some forums focusing on older games, praising the Baldur's Gate remakes may lead to this.
While most of the fandom loves Big Boss, there is a section of fandom that feel like that he's getting too much attention lately, not to mention the choice of not asking David Hayter to resume the role of the character.
Kojima's writing can be highly divisive - many people love the philosophical chatter and silliness, others think that he's pretentious and need an editor to rip into his script with a chainsaw.
Castlevania fans are HIGHLY divisive. There are basically three camps: Pre-IGA fans, IGA-era fans, and Lord of Shadows Fans.
Then there's Castlevania Judgement: You've got the people who dislike Castlevania Judgement completely, the people who dislike the character redesigns but like the rest of the game, the people who dislike the redesigns but wouldn't have minded as much if the characters got their classic appearances as alternate costumes, and the people who simply view it as a fun crossover.
Game Shark/Action Replay/ Powersaves. That is all.