I play pretty much every day, and I'm still quite engaged. Of course, I have other games to feed my RP/social jones (Defiance is really bad at this, despite some improvements to their social and chat tools). It's not an MMORPG, it's an MMOTPS...so while I wouldn't want to have it as the only game I play, it fills a niche superbly. Despite being "massively multiplayer," the game plays as smoothly as any conventional multiplayer shooter, with terrific movement, real-time (collision detection) reticule aiming, minimal lag, and gorgeous graphics. If you like that kind of combat, this game does it superbly.
It's a pity, really, that the social/chat tools are so minimal, as the game world can be very immersive and the TV tie-in is a fun concept, reasonably well executed. The writing's pretty good, too: cutscenes are at least as good as SWTOR (although not in the simply unmatched league of TSW), and there's a lot to do. It would be a great game for roleplayers...if it weren't so damned hard to talk to each other. The dumbing-down of the interface that console ports suffer from kind of killed it for RP'ers.
The upshot? I like it and play it regularly.