I've been playing this game here and there since I saw their booth at AX...2...3 years ago? I can't remember.
It's an interesting game, and it is fun for a while, but the biggest problem is that there's not much to do.
The world is fun to explore, especially when equipped with jetpack/boots/whatever, but there's only so much of it.
Beyond that, it quickly becomes a grind, and as such quickly gets boring.
They introduced a good deal of dynamic events and such to try to keep it interesting, but they don't change much.
The end/world boss seems interesting, but every time I've attempted it the game lags so bad, seemingly due to the lack of optimization on the server end to deal with so many players in a compact space. I usually die long before I know what even hit me.
TL;DR: It's a good way to kill a little bit of time if you're bored, but if you're looking for a serious game to sink your teeth into, look elsewhere.