Great gameplay and a fun and addicting theme (find and grab orbs) the missions are the same but get sort of harder and until you level up you won't have alot of fun (but finding orbs is alot of fun) Basically it's a fun game once you are leveled high enough. Co-op is tons of fun and has some replay value. Of course the main reason this game will shine in the future is:

1. It's got some great concepts, Another game like this could nail it right on the dot
2. Halo 3 beta...duh!