I think Manziel's success will be determined by how well he takes to NFL coaching. That go for the throat, never give up style can win you some games if you're able to keep it in check until you really need it. If you can't, you create too many turnovers or get injured yourself.
Personally, this year's crop of QB's wasn't very good. Manziel is the only one of that group who could actually be special. If you're going to be fired for your QB choice as a GM, might as well swing for the fences.
Oh yes, Clowney will continue the proud history of pass rushing DE busts at the top of the draft.