These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Broken Base: While a majority of the fans of the series consider MvC2 to be the best incarnation of the game so far, a good portion of fans, specifically those put off by the latter's steep learning curve and seeming imbalance, prefer the older entries.
Light blue Venom. It may have been a mistake or stylistic choice, given that his alternate color is in fact black, like the one in Marvel Super Heroes. However, has anyone seen a light blue Venom outside of Marvel vs. Capcom and Marvel vs. Capcom 2?
Orange and blue Spider Man.
The weird alternate colors were mentioned by a Marvel vs. Capcom 3 developer in one of his blog posts:
"Remember Gold Storm from the comics? Thought not."
Designated Hero: This game has the subtitle New Age of Heroes, and includes M. Bison, Shadaloo-era Cammy, Akuma, B.B. Hood, Tron Bonne, Servbot, Dr. Doom, Thanos, Magneto, Juggernaut, Sentinel, Spiral, Silver Samurai, Omega Red, Sabretooth, Shuma-Gorath, and Blackheart...
Ear Worm: The character selection song. Gonna take you for a ride *do do do do do* , gonna take you for a ride *do do* ... Repeat until your brain melts. Best part, it's back for Marvel vs. Capcom 3.
The competitive scene uses nicknames for several commonly-used teams. Aside from acronym names (such as MSP for the team of Magneto/Storm/Psylocke) some of them include "Santhrax" (Sentinel/Storm/Captain Commando, named after competitive player Sanford), "Scrub" (Cable/Sentinel/Captain Commando), "Matrix" (Storm/Sentinel/Cyclops) and "Clockw0rk" (Sentinel/Strider/Doom, after another player of said name).
Marvel vs. Capcom 2 in general has a much larger competitive scene in America than in Japan. This is justified, since half of the cast was from American comic books and that was one of the reasons why Capcom decided to create Tatsunoko vs. Capcom, so Japanese players can have something they can relate for.
Played straight in the Philippines as well where the game still sees regular play in the arcades, even with its sequel already available.
Good Bad Bugs: Or more precisely, glitches, in this case. The game was so poorly put together (one porting team stated that its code was held together with "string and glue") that glitches became an integral part of competitive play. This lead to a unique situation where the competitive game is still growing since glitches can lead to new strategies and tactics that are countered by even more glitches.
Hilarious in Hindsight: The infamous MAHVEL BAYBEE video takes a new meaning when you remember that Marvel made a deal with the NBA. Sadly, there's no Mango Sentinel for the New York Knicks in this one.
Magnum Opus: Of the entire Marvel vs. Capcom series. To this day, 14 years after its debut, there is still a thriving community for this game.
Mexicans Hate MVC2: Zig-zagged: While the game is still played as much as is played in the U.S., it's also disliked in Mexico for the same reasons already mentioned (unbalance, copypasted characters, lame final boss, etc), if not even more, not to mention the arcade machine didn't reach to many Mexican arcades as their predecessors did in the past, partly due to its price.
Nightmare Fuel: DEAR GOD, ABYSS...His second form might be worse than his final one.
Porting Disaster: The PS2 port is very disliked, due to the game having many of the small Good Bad Bugs and glitches utilized in tournament play being nerfed or removed outright.
SNK Boss: Abyss is a surprising subversion. Oh sure, he's a cheating bastard like the rest of his fellow Capcom vs. Whatever bosses, with stupid high-offense and no hit-stun, but he's surprisingly easy to beat regardless unless you have an all-melee team.
That One Attack : Cable's Air Hyper Viper Beam. No Delay, Insane priority, easily comboable, spammable, and chain into itself. You can basically do a massive combo just by repeating this move.
Tron Bonne's drill attack. Comes out quickly, deals lots of hits, great range, and easily spammable. Drill, baby, drill.
On the Assist side of things, we have Captain Commando's Captain Corridor. Comes out quickly, has insane vertical range, and is invulnerable for the first few frames of the move. No wonder he's one of the top Capcom characters chosen.