UFC Undisputed is a very good fighting game that's even more fun with friends, a great way to get into MMA if you've never watched it before.
What the devs did right:
1) Easy to learn, hard to master - anyone can pick it up and score big knockouts. Then you start learning about counters and the clinch and the ground game, which is surprisingly deep.
2) Decent roster - 80 fighters, all more or less authentic to their real counterparts. The champs are scary, but not invincible.
3) Fully licensed - Dana White and the UFC are behind the game 100%. It feels like a pay-per-view event, from the music and commentary to the refs and the ring girls.
4) Mostly pretty - The graphics are generally pleasing and the animations tend to be captured well. Points for Anderson's quick kicks and Chuck's overhand right.
What they should improve:
1) Slow, clunky UI - a game's interface should never be a mechanism for punishment, nor should you allocate second-rate devs to its design and programming.
2) Create-a-fighter nags - I want to train more and fight at the lower ranks for longer, gradually building up my characters so they'll actually have a chance by the time they fight the top 5 in their weight class. Also, some of the grappling tasks in the camps leave too much to random chance on the AI's part. Make it more controllable and skill-based as opposed to getting lucky. Finally, I think unlocking the components of a gym with one fighter should carry over to subsequent fighters, gives you a reason to keep playing and trying new styles.
3) More fighter individuality - let's see Koscheck's cannonball shots, Rampage's turtling before counters, and so on.
4) Occasional graphical ugliness - collision is somewhat janky, and some fighters look unrealistic or just plain bad. That can be fixed.
So yeah. Both versions seem to be holding up well, no Fallout 3-esque failures so far. Best Buy has a good deal - a free ($15 or less) UFC DVD, 10 off the next live pay-per-view, and a $10 Best Buy gift certificate. This shows that the UFC is willing to help get the game out there to the public and hopefully augment the proliferation of MMA in the states.
I recommend the game to anyone who likes fighting games, any MMA fan, or anyone who wants to learn more about the sport.