Individually, the X-Men might not be able to hold a game on their own. Hell, even X-Men Legends II: Rise of Apocalypse has a few glaring problems, but when it comes to working as a team, this game's got it where it counts.
From the massive roster of both heroic and villainous mutants, you can have up to four running through the overhead levels at once. The gameplay's basic stuff - follow maps to mission goals, then blow up or beat up whatever's in your way. You'll gain experience points, adjust your mutants' abilities and watch a clichéd story unfold, but with four people in the room fighting together, the sum is much greater than the parts.
Performing special attacks simultaneously bumps up the damage, so calling out something like "silver dude! Hit him now!" lets your pals know to bring the radioactive pain down on one target. It's all about moving as one unit and listening to someone who knows what's up, rather than going off and doing your own thing. Cyclops hangs back, shooting optic blasts while Juggernaut or Colossus head in for a beatdown. We couldn't help but throw Wolverine into practically everything, because hey, he heals fast. Sorry, whoever plays as Wolvie - you're the regenerating tank, get used to it.
Legends II may involve a lot of stat-tracking and menu-surfing, but when the team comes together, everything shines. Playing it on Xbox Live is one thing, but if you're fortunate enough to sit three friends down in one place and devote a night or two, this may be the best superhero team game available.
So, why not Ultimate Alliance? Because the entire Marvel universe isn't a team, and hugely powered heroes like Thor and Silver Surfer could handle most of the bad guys by themselves. Such balancing takes away from the character's true power, thereby making it a compromise, not an authentic representation. The X-Men are a team, and need to be if they're going to stop villains like Magneto or Apocalypse. Ultimate Alliance may be the better game, but it's surely not the most on-target.