I only tried the multiplayer, since it was free on valve for a weekend about 1-2 weeks ago. And I must say I am very disappointed with the support the game is getting, and with the community.
Every second server I got in had someone with some sort of a hack going on, games would constantly be shut down due to host leaving and it not being able to transfer to a new host, and every once in a while we would have the maximum amount of players and the game wouldn't start (would just say "waiting...")
I am most disappointed with the community. Every single server had people dropping various racial slurs, and comments regarding the sexual orientation of whomever killed them. The maturity level just did not exist and definitely made it a less enjoyable experience. Then I went back to good old TF2 and the maturity returned
I would say the game had lots of promise and was quite entertaining, but having no direct control over what map you would play on (and very limited amount of maps) also took away from the multiplayer experience. An extra note: Who ever hosted an online match had the advantage of zero-lag and therefore had the edge in sudden run-ins. (which is awesome when you are the host... but there were times where I would turn a corner, put 3-4 shotgun blasts point blank into someone and I die, I watch the replay and I didn't even get the first shot off)
Final opinion: I would not buy it. It was fun to play for a weekend, but by Sunday I already uninstalled it even though I had the day left. I'm sure the single player is much better and would be fun, but since the game (and many games like it nowadays, sadly) is made for the online gaming and will just dissolve when the next one comes out; it would not be worth it.