Been playing this since December and totally hooked. It definitely had (and has) its share of issues, but if you are the slightest bit of a Fallout fan it is worth a look right now.
It is basically co-op Fallout with a light survival/building element and while you can easily solo it is a blast with friends. The community is very supportive as well.
If you want to see some good coverage of what the game entails, watch some Youtube vids from norespawns, Final Render, JuiceHead & Darth Xion.
My biggest hope after playing this is that Bethesda takes this tech and makes a co-op ES game down the line. For me that would be a dream come true.