They've got personality, or at least Tyler and Earl have, and that goes a long way for me. Tyler for example isn't technically very impressive but his voice is so distinctive and, while his image is obviously contrived to some extent (whose isn't?) there's a certain irrepressible anger and energy to his delivery/lyrics, which can often result in his lyrics not actually making much sense... but then he'll say something which you'll never hear another rapper saying. I really like Tyler's production too, and Left Brain's. Mellowhype 'Blackenwhite' is probably (as Tyler has said) the strongest O.Future release to date (although I also think the first ten or so tracks on 'Bastard' are really strong, it tails off a little bit for me) - at least of what I've heard.
But Odd Future as a complete collective aren't exactly uniform, I suppose its the production that unites them, but they don't represent a defined aesthetic like Wu Tang and to be honest for me they are nowhere near as compelling (on the whole) as the Wu MCs. Mellowhype are a much more straight-forward rap-group (Hodgy is actually possibly the strongest rapper from O.Future technically aside from Earl), 'Rolling Papers' by Domo Genesis is more-or-less Wiz Khalifa style weed-veneration. Domo is alright, but I can't really see him or Mike G ever becoming big off the back of their skills, Odd Future's popularity is obviously tied in hugely with their image/Tyler's personality. Tumblr is awash with photos of Tyler. Tyler's music, however, is worthy of making a splash IMO. Earl is a very good rapper but again I think it was the production on 'Earl' that made it so successful.
Actually there's a lot of rappers around nowadays who aren't technically impressive in terms of complex/interesting lyrics but who still make good music, because they pick good beats or because they know how to work with the beats they have so well - Wiz Kalifah is the obvious example for me. Curren$y sort of hits me in the same way but he's a technically good rapper as well, I just think the laid-back lazy delivery of his lyrics merges so well with Ski Beatz production, it just creates a great sound.