I went ahead with the 'all of the above' option, since I couldn't narrow it down between the options given. If I had to pick a single favourite element of zOMG!, it would likely be the ring system - it's essentially just like the avatar system (with lots of mix-and-match customisation), if only your avatar's pants could shoot lasers. Now that may seem like a minor difference, but some of us appreciate the little things in life. wink
In all seriousness, zOMG! hits on something fundamentally Gaian; being able to define yourself - and re-define yourself - with just a few clicks of the mouse is part of what keeps people coming back to the site in general, and it's what I think stands to be the biggest draw for zOMG!. There are a few hiccoughs keeping it from doing that effectively right now (the ring effects don't 'match' very well, and aren't particularly evocative), but the underlying principle is still perfectly sound.
zOMG! also does an excellent job evoking Gaia's community aspect through its gameplay, which is probably its biggest draw as-is; as a Forum, Gaia puts a big emphasis on socialization, so the opportunity to actually get in and play with your friends is a huge plus. And that's not really a coincidence, either; all of the things that Gaia's about are what zOMG! is (trying to be) about. In general, I think it's fair to say that Gaians like zOMG! for the same reasons they like Gaia - at their cores, the two aren't really as different as they might seem...