The "hammer time" mini games & the 2D side-scrolling cartoon style platformer where the best of those.
Theres gonna be a ton of crappy stuff,... and some really well made stuff.
There needs to be a scoreing system, and a way to catagorise stuff and sort stuff.... so you can find the well made content others have made in it.
This video showed the scoring system.
Predicted 15+ million lifetime-sales for God of War: