I've been a fan of these games since Knockout Kings back on the PS1, then Fight Night 1 & 2 on the PS2. Unlike many on the EA Sports annual re-hash games, this one has kept getting better.
The graphics are stand-out, and seeing this running in a shop was one of the things that led me to buy an Xbox 360. The sound matches, with the crunch as your fist slams into your opponent's face in slow motion being particularly brutal.
Bouts are fought hard and fast, and the removal of the hud for this version only enhances your involvement. The character progression keeps pulling you back, and I wasn't satisdfied until I'd taken a charecter to the top in every weight class and unlocked all the extras.
This (along with Test Drive Unlimited) is my most played xbox 360 game, and you can't say fairer than that. It's one of the reasons to own the console!