Fun for a bit... but gets repetitive
The method of fighting will discourage the avid fighting genre fan. You can win with button mashing, instead of delicately planning out your attack to overwhelm your opponent. This is especially true in online mode, where you'll face opponents who generally will not counter as much as computer controlled opponents, so you can mash on the punch buttons and pull off some pretty amazing looking combos. The counter move system is actually one of the better aspects of the game, and one part of the game that requires more skill than most, as you have to see what move their throwing at you and time your counter accordingly. It's a very simple yet surprisingly effective system. The grapple system, though, seems border line broken. It takes a frustratingly accurately timed button press to pull off a move that in the cases of most fighters isn't even worth it.
The fighters in this game are actually pretty well varied, and you'll have to adopt a different style with each if you want to play really well (though each fighter you can get away with button mashing, which is, again, pretty dissapointing). They look and move great too. Cartoonish? Yeah, kind of, but for this game it works.
The different environments you can fight in are all pretty different from one another, though not one really stands out. A couple are multi-tiered and can have you or your opponent crashing through a wall or glass or over a rail and go crashing down some stairs, though in a single fight it's rare that you'll get to see the entire level.
As you can probably tell, the variation in this game is a main selling point. The characters and environments all help add to this, but where it really hits home is with all the different game modes. There's the standard story mode, which never really tells a story by the way, save for a few different cut scenes for each fighter at certain intervals. Add that in with a time attack mode, a survival mode, and a generic "jump righ tin and start fighting" mode, and you have plenty of variation right there. Couple all that with the fact that most can be played in either single or tag format and you have a pretty impressive selection at your hands. Playing through all of these will be most beneficial to you as they'll unlock certain goodies like new characters and outfits. A side note on the new characters, though, none of them have their own story mode attached save for one, and their moves are pretty limited too.
The multiplayer aspect is probably where you'll get the most enjoyment out of this game. Button mashing, sure, but it's still always more fun to beat the crap out of a buddy than a computer controlled robot. With support up to four players, it can be a pretty good party game. Online is actually pretty stable, a few moments of lag here and there, but that could be caused by any number of things.
So in all, this game would be a great game if only it was, simply, more fun for a longer time. It gets pretty old rather quickly and will probably have you tossing your controller around in anger more than a couple times. But if you're looking for a good multiplayer game to show off your console to some buddies, this game will work great.