As a UFC fan I looked forward to this title. After renting it this is my experience...First, you enter in your height, weight, etc. You complete a serious of tests to determine your level. Jumping jacks, sit-ups, push ups and more. (I would suggest a leg strap to hold the controller.) My out-of-shape self found this alone to be a good workout. Once finished you are free to choose a trainer to workout with. You have several trainer options. Unfortunately, like others have stated, it suddenly freezes up in mid workout on the Wii console. Please be cautious I have heard people have had it ruin the Wii console. Fortunately mine still works with no issues. I hope to try this for XBOX 360/Kinect very soon.
You need the leg strap (ie from EA Sports Active 1) that you can slip the nunchuck/second remote into. Without it, the majority of the game is useless. Unfortunately, I sent my SA1 leg strap to my nieces when I bought SA2, so I wasn't able to fully experience this game.
What I was able to do was a good, solid game with great, butt-kicking exercises. If you have a balance board, it makes the game THAT much better.