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.
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?"
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 torn 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, the lack of third party support as far back as N64, the kiddie/family stigma 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. In fact arguably most major debates revolving around console gaming have Nintendo has 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.