Facebreaker- break his face, or more likely, your controller.
With any fighter, be it boxing, 2D or 3D Tekken-style, there's two basic types of play, vs a human or vs the CPU. Facebreaker's biggest problem is it can't decide what to go for and falls straight down the gaping chasm in the middle. If beating the tar out of a cpu opponent is your bag, you'll mostly have to play the Brawl For It All mode, where you face boxers in a set sequence in a bid to conquer venues and win belts. Sadly, however, rather than make this a proper gamemode in its own right, the developers have chosen to make the mode a sort of glorified tutorial. So once you get a few fights in, you'll face opponents who will beat you like a government mule until you twig the single strategy that you're meant to use to beat them. Helpfully, the game will tell you what to do before your third try. Unhelpfully, it then kicks you back one match if you lose again.
The effect of this boneheaded design decision is devastating. If you struggle to get used to the exacting timing needed for one opponent, you soon find yourself facing the previous one again, often needing a radically different playstyle. Lose to them, and back you go again. And given that a basic punch combination in Facebreaker is delivered by hammering a single button at the speed of a hummingbird's wingbeat, fatigue and frustration set in fast.
Facebreaker's core boxing engine is actually quite good and fairly deep. There are dodges, blocks, parries, power attacks and throws, and the defensive system feels natural and is easy to pick up. Some characters are of such radically different sizes that a 'low' punch looks high or vice versa, but that's not a problem unique to the game. And those characters are at least pretty diverse and get messed up well by repeated punches. Between rounds, you see the fighters shaking out the cobwebs in the corner, which can be amusing, and there are pre- and post-match talking heads which add character. The ditzy ring-girl is probably a love-hate thing.
One thing that deserves a mention is the vaunted 'boxer factory', which allows you to take a face and map it onto a boxer body. It's an amusing idea, but the available outfits are very limited (you basically just change the color and texture) and created boxers look very odd compared to the ready-made ones. Ladies will find the choice of only two female boxers to work with very limiting, especially since one is effectively a midget and makes your character look about 12. There's usually only one special ability setting one boxer apart from another anyway, so it's all in the cosmetics and they're not up to much.
Multiplayer is well supported, with a few modes and online play. I've not tried it myself, but given that the timing in Facebreaker is extremely tight, I would expect any lag at all to be utterly fatal to the game online. Then again, I've not yet played an online fighter that I thought worked, so if you find Tekken or SC4 work that way for you, it may be worth a look. In the end though, Facebreaker is a characterful, good-looking game, crippled by some terrible design decisions and a much-hyped feature that actually adds very little to it. Rent or avoid.