A slew of Marvel character nostalgia, intriguing story, and excellent Xbox live play make this worth checking out!
Raven Software does a great job of coming up with a great storyline (which I will not spoil here), also allowing you some options to make some choices to change the path of the story (though maybe not as much as they initially let on).
To give an idea of the scope of the cast involved and people you will run into, the game touts a cast of over 120 Marvel characters, good and evil. Before you jump out of your seat, remember: only slightly over 20 of these are actually playable. You will be pleasantly surprised at some of the good and bad guys that you will run into along the way. More popular villains like Dr. Doom and Bullseye are instantly recognizable, and then there are some more old school/less known villains like Fin Fang Foom.
Graphically, you could say MUA actually looks a bit dated. While you can easily recognize your favorite characters and villains, it really does not quite feel like a next-gen offering. This isn't to say its a bad game, but graphically, the 360 (and even the PC version) could have looked much better considering the technology. Level design is another area that seems to be lacking slightly at some points in the game. While there are definitely some really great locales (ie Atlantis, and Arcade's Murderland, Stark Manor), some levels do get a repetitive feel after playing for awhile. Sound is a pleasant surprise. The music does what it needs to do, and keeps you immersed in the game. The voice acting is rather well done, with some really big names contributing to the voice over cast. While some may almost sound over the top, it fits the evil villain/sarcastic antihero rather well.
Gameplay is where MUA really shines. Each character looks, feels, and plays very different from their counterparts. Throw in the ability to unlock at least four costumes per character (which change your stats and provide a new way to play the character, different abilites, etc) and you have a slew of options and different things to try. The story is engaging and fun, and will surprise you and keep you wanting more right up to the rather epic end battle. The ability to bring MUA online and form a team of heroes with your friends and go through the story mode is a really wicked feature. The longer you play as the team you created, your team will get specific experience and bonuses, and notoriety which you can show off online to other "wannabe" supergroups. While the game offers somewhat branching storypaths, replay value on this game (as far as playing single player) isn't all that high. However, taking it online with your friends and going through the story mode undoubtedly gives more reason to keep playing. With the potential of XBLA's ability to open up more characters for future updates, MUA has a lot of future potential.
Overall MUA provides an excellent foray into the Marvel Universe as a whole. For the comic fanatic there are endless hours of fun to be had here. There is a Marvel Trivia portion of the game, a combat simulator that simulates historic battles between certain superheroes and villains (spiderman vs lizard, iron man vs mandarin, etc), that add some flavor to the game. There are plenty of achievments to unlock for the point fanatics out there as well.
Marvel Ultimate Alliance is a fun ride in the marvel universe. While graphically it may not feel quite like a next gen game, the huge cast, great story and the ability to play as a team with friends really make it something worth a look, especially if you enjoy the Marvel Universe.