Highly underrated. Very simple, but deep enough to be a lot more fun than than a lot of other fighters out there.
The difference between a good fighting game and a bad fighting game is it's "depth". If the more you play a fighting game, the more unfullfiling, simple, and repetitive it becomes, the more shallow it is. Like Mortal Kombat Deception for example. If the more you play a fighting game, the more strategy you discover, the more counter tactics you discover, and the more you're forced to think critically, the more deep it is. This game is the latter.
And it's all about the stamina.
While it appears to be true that you can make anybody tap out or tap out yourself at random due to the lack of control over submissions once they're applied, it isn't. Mashing buttons will counter submissions or takedowns, yes, but it isn't quite that simple. The more you attack with strikes for the knockout, the more your staminia depletes. The more your stamina depletes, the more likely you are to tap out. If you charge at your opponent swinging like a lunatic to knock him out, chances are he'll be able to make you tap out easily. Conversely, the more you bide your time and pick your punches, the more likely you are to wear your opponents stamina down, at which point you can apply a submission of your own for the win. And that's barely the tip of the iceberg.
The groundfighting is simple, but works very well. If you're on top of the mount, you want pummel your opponent and score a KO, or wear his stamina down for the submission. It's easiest to do this from a full mount, when you aren't in your opponent's guard. The opponent however, will be making this difficult for you by punching and kicking off his back, covering up, trying to get you in his gaurd, and countering your punches and rolling you over so that he is the one on top of the mount, in control. You're constantly jockying for position whilst trying to get in a shot, or apply a submission. Simple, but nailbitingly good. And there's more.
You may need to play the game for a good few days on the hardest difficulty before you find the depth, but once you do, and your friends find it too, it suddenly becomes a great game, and everything makes sense. It's not "random" or "shallow" any more, and you'll be thankful you bought it.
It's not everything a MMA game should or could be, but for what it is it works very, very well.