My reaction to the Yoo memo is almost the exact opposite of Emily's : I'm struck by how lawyerly it reads. It cites tons of authority, hedges arguments, discusses counterarguments, and generally reads like a careful lawyer's work. In fact, if it were a Supreme Court opinion rather than an OLC memo, I believe it would be entirely acceptable under Jack Balkin's theory of living constitutionalism. (Or so it seems to me—I remain a bit unsure of what Jack's theory rules in or rules out.) As Jack might say, Let Yoo be Yoo!
Instead, I think the problem with the memo is that the quality of the doctrinal analysis is generally poor. At least that's what I've been struck by in the sections that touch on the areas I teach. Take the discussion of the necessity defense and self-defense. I think it's probably right that in a genuine, real-deal "ticking time bomb" scenario, there could be a necessity defense to torture in some way. But while the memo notes the doctrine is fact-specific, it weirdly does not explain just how narrow those circumstances would have to be for the doctrine to apply. You end up with a chunk of the memo saying there's a possible defense "depending on the facts," but without explaining that those facts would have to be pretty extreme to matter. That's the impression I get from the sections I know well, at least.