If you're a fan of the franchise or just want a simple button masher Shrek SuperSlam is easy to recommend.

User Rating: 7.1 | DreamWorks Shrek SuperSlam XBOX
I've oftened eyed Shrek Superslam sitting there on the shelf of my local game retailer and pondered picking it up, but as the price was sitting at over $50AUD I just couldn't bring myself to pick up what I've heard's a relatively shallow game. However, I managed to find it cheap elsewhere for $20 so I bought it.
And for $20 it's worth it. The gameplay is rather shallow.
It usually boils down to button mashing.
There are a few rather simple combo's you can learn, but just mashing buttons usually achieves the desired result. The graphics are bright, colorful and attractive. They won't win any awards but you can't call them bad.
The "fully destructable enviroments" it brags about on the packaging are laughable though, cause theres very little in the enviroments to destroy and doing so has little effect on gameplay. The music is serviceable.
And while the original voice actors aren't used the imitators are reasonably spot on, save for Donkey's I reckon.Theres quite a few bit's where he sounds off.

The main reason to pick this up would be for the multiplayer.
It's not particularly engaging but you get a few friends and you can easily while away an hour or so smashing fairy tale characters around the place.

Basically, if you can find this cheap I'd say pick it up.
It's not all that bad.