Perhaps unsurprisingly, this review by John Lott is quite misleading. Under Choi & Gulati's citation-based measure of judicial quality, Alito comes out very poorly, well down in the bottom half of all circuit court judges. That was their primary measure, and Lott doesn't mention it.
Lott, cherry picking? Who'd have thought it? Lott defends himself in later comments (under his own name, even!) . I haven't read Choi and Gulati's paper so I don't know for sure who is right here, but I know who I would bet on.
Update: Zywicki has a followup post with a couple more comments here.
Tim, what happened to your comments on the thread on the Volokh thread? I thought I saw at least one post from you there.