Not much to review about Adventure Comics #0. I like the cover a lot on an artistic level, and I'd love to see Aaron Lopresti on a Legion book based on this cover.
Yes, the costumes on the cover don't match, but I can easily forgive that since (a) this isn't a full reprint book and (b) it's kicking off a new series and they want to have recognizable characters on the cover.
However, it's an EPIC FAIL for what it's supposed to be replacing. On the original cover, the Legionnaires are voting NO against Superboy, telling him he's not worthy of their group. On this one, Superboy's just standing there, we see only two of three name plates, and we don't even know that those are yes/no lights.
Not much to say about the interior. It feels weird to see the dots for colors like in the olden days, when it's printed on good quality paper and the backup has modern coloring. My only real gripe is that they have used the retcon coloring that shows Brainiac 5 there (page 5 panel 3 and page 11 panel 9).
The backup story is unrelated to the Legion, it's a lead-in to Geoff Johns' "Blackest Night". Nice to see Francis Manapul one more time, though.
The back page has a small reproduction of the cover to issue 1, coming in June. It is reminiscent of the Deja Vu covers like we saw on Adventure (v1) #300. The figure in the middle is blacked out, but it's most likely Kon-El as we saw on the last page of the backup story. But that looks like Starman in the upper right corner.
Also: IGN reviews the backup story, while Comic Book Jesus reviews the whole thing.