Oh, I'm totally cool with someone diving in and doing a full review on anything they're comfortable reviewing. I'm hesitant to have any sort of officially tiered review system as that might slow down reviews in general (or give me an excuse to ignore things that aren't prereview+).

Maybe encourage people to do mini-reviews for functionality and compile checking and such. They can poke at it, and if it looks good, just comment to that effect - else, mark it review- with the problem they found.