Defiance is a downright amazing game, running gunning, dodging using cover, everything you need in a shooter but with MMO elements. Ripping around in vehicles, running over mutants. Haven't experienced any Arkfalls yet (Defiance's Rifts). The PVP is instanced. Apparently you can get healing and shield buffing guns later in the game. Finally somebody made a decent SciFi game. Its buy to play with a cash shop that only sells cosmetic items and boosts.
If you like SciFi and shooters or just want something a little different then I suggest you try it. The only downside is the console port UI.