2010 Morewood Enza
The good thing about this frame is that for 4x hardtails, I don't think it can be beat! It's ridiculously stiff, sprints super fast, and is really stable in the air. Plus, the square tubing on the downtube and rear triangle make it look 250% beefier than any other hardtail out there.
The bad thing is I get made fun of for riding a pink bike. But seriously... Nothing.
I guess my review is kind of in "The Good" section. If you are serious about 4x racing, buy a frame that's designed to do just that... The Enza.