Ryan is such a terrible choice I really don't know what to say.
He will help secure a bit of the party base, the fiscal fanatics, that Romney already was at least tolerable to, but will end up hurting him with the religious right. Won't help at all with the moderate middle muddle, won't bring over any left wing defectors, has not election pull in any specific states, and will be useless after the election.
I'm left wondering if Romney tried to pick somebody who would make him look good in comparison. Somebody who would pull some of the flak off Romney, by acting as a target. Sort of the Dan Quayle theory of VP selection.