You played a stunt plane that would fly through hoops and around obstacles. The game featured a lite physics destruction model where if you made a mistake it would blow to pieces and tear down whatever you ran in to. Not as part of the gameplay, but in order to make your inevitable mistakes more entertaining. It featured user editable replays and a level editor, so people could post and rate content. I guess you know where this is going...
Probably 50% of the levels and replays turned out to be something along the lines of "9/11 simulator". I culled it manually as best I could and eventually turned it off. I found it pretty funny how much of a cesspit user generated content turned out to be (in the same way that you'd laugh at 4chan), though I do wish I spent the many weeks rolling it out on something else.