X-Men: The Official Game has a control scheme that takes a little getting used to, but once you do, it is surprisingly easy to perform complex attacks. Unfortunately, the slippery control the actual commands provide renders any gain provided by the scheme null and void.
You move your characters around the 3D world using the W-A-S-D keys and your various attacks and abilities are performed with the L, K, J, I and O keys. So basically, putting your hands on the keyboard as if you would type, your left hand moves your character, and your right hand is for your attacks. Again, this took a couple of levels to get used to but when I got into it, I had no problem performing the attacks... now accurately aiming and dealing out damage was another thing (but that goes back to the slippy controls, not the button layout).
So what happens when you press the right hand buttons? As you would expect, different things based on which mutant you are controlling. For instance, the J key will let Wolverine perform a quick attack, Iceman shoot out ice beams and Nightcrawler punch, where as the K button lets the blue-demon teleport to an enemy, Iceman unloads a fury of ice and Wolverine deals out a wider attack that does less damage but can effect more enemies.
Ultimately, X-Men is an OK title with a few nice features, but isn't really worth the effort. If you feel you have to play it, rent one of the console versions.