In order:
1) It's like Destiny+Diablo+Mass Effect, with flying and more than one power per class.
2) It's flight system and gunplay are perhaps the most fun I've had in the genre. The classes all feel/play very different but all stay viable at higher difficulties. I also think the core story is stronger than Destiny's, but it's still primarily an Excuse Plot to build the gunplay around.
3) It's got a lot of bugs to iron out still, plus some questionable design decisions like inability to revive yourself, lack of waypoints in freeplay, and needing to run all the way back to the forge to launch missions. A number of these are slated for patching or redesign, with a major patch dropping Tuesday. The primary issue right now though is a dearth of content, and it's particularly damning that there's no real reason to run Grandmaster 2 and 3 just yet - the amount of extra time and difficulty aren't currently worth the rewards you get from doing so.