Steep learning curve, but totally worth owning your opponent!
You might feel utter frustration in the first few hours of playing the game, but as you perfect your skills you will find more and more enjoyment in it.
The game also has a money system in it. By fighting in ranked servers you earn both belts (indicates numbers of fights you've been in, not really related to skill) and TC (tori-credits) which you can spend to customize your character. To earn great amounts of TC, you can join tournaments and/or bets. You can also win duels against other consenting players to get their money in a pink-slip fashioned way.
A major upside to the game is the vast amount of mods it features. There is anything from aikido, judo, taekwondo, boxing to gorilla fights, bar fights and parkour. Literally, hundreds of mods!
Since this game is one of a kind (and free), I highly recommend at least trying the game.
PS
If you're new to the game, stay in the noob servers (for the sake of your own nerves).