This game owns.
http://www.youtube.com/watch?v=4XvxNCyUGJkHere's what online's like
http://www.youtube.com/watch?v=rroWM9u2S4k#t=0m10sforget mario, this is the only game that's worth owning on the Wii. This is the reason I bought a wii 2 years ago. No regrets.
Long ass teeth grinding fights? Check
Huge assortment of unique bosses? Check
richarding around with friends online? Check
Multi-boss brawls? Check
Customization? Check (well, as a side reward for killing stuff)
Yahtzee hates this game? Check, he played it for an hour. The tutorial is boring? No stuff?
Level up system? Nope.
This is a game where armor, weapons, pigs, etc. are all besides the point. Your success is explicitly tied to how good you are at the game. People can go out and beat the stuff out of monsters naked, with a mediocre starting weapon, without taking any damage throughout the entire fight. Furthermore, this game is hard. It's not Peggle, it's not Mario, it's a game that throws a giant loving raptor at you just to see if you'll get your ass kicked (and you likely will get your ass kicked the first time around).
Also if you do plan to buy it, the dual shock controller might be worth the extra dough as well.