Ah, that douchebag.
Aren't they all?
You're forgetting the sacks of crap, and batshit lunatics. Ryan feels like a douchebag to me.
He's not a terrible choice insofar as Romney's campaign of avoiding taking definitive stances on issues and criticizing Obama was unlikely to go anywhere. So, now he's adopted Ryan and his budget and accompanying political views as a central issue in his campaign. Obama is still the heavily projected winner and as time has gone on that projection just gets more and more likely. Romney needs something... anything... to change the flow of election.
This isn't like '08, McCain was a strong candidate -- who I think would've made an outstanding president had Karl Rove not existed in 2000 -- and while probably would've lost regardless of Palin, that choice simply drained him of credibility among the intelligent voter.
Romney doesn't have much in the way of credibility to begin with, his willingness to shift positions based on political expediency and his liberal-styled government in Massachusetts makes it hard for most people to take him seriously. His value is that he's not an idiot or openly offensive, and "looks the part". What he thinks he needs is someone who's more... impassioned... to actually make anyone give a damn about him or his campaign beyond "anyone but Obama" style politics. Which doesn't really work with moderates, as evidenced by Bush.