A group of us downloaded and started the open beta yesterday. So far, I think of this game as a combination between Borderlands and Planetside. The game is heavily focused on crafting upgrades / weapons etc and exploring. The crafting portion of the game was particularly interesting to me - there were a lot of options and paths to get something new, and the mechanism was rather unique to do it.
The PvE portion of the game was really fun, it held our squad together fairly well. Despite differences in game time, we could all do any objective we chose.
The PvP portion of the game is an "eSports" game that reminded me of bombing runs from UT2k4 based on videos on the site.
Check it out here: http://www.firefallthegame.com/about