In regards to Aliens: Colonial Marines...
No, it's not the best game ever. Yes, many aspects of it are disappointing, especially since I had high hopes for the game, being that I'm such an Aliens fan.
However, I don't believe it's anywhere near as bad as it is being made out to be. I know the trolls are in a feeding frenzy over the game, but I'm actually enjoying it quite a bit. Really, I'm having fun with it. What I'm most disappointed in is that they didn't have many cooperative multiplayer modes. Hopefully those will come with future DLCs, but it really should have been the primary focus of the game instead of the versus modes they have, which I don't think are too fun at all.
But anyhows, while I can't recommend it whole heartily at the current price, I think it's worth considering if the price comes down, and a lot, during a steam sale or something.
Speaking of a cooperative game that is awesome, though is Syndicate from EA, which I also got recently. While I was leery at first, since I loved the original back in the early 90's and they made this a shooter instead of an isometric strategy game, I gotta say it's pretty great, IMHO, especially the coop mode. Only problem is that not many people are playing it, unfortunately, so that finding other players isn't always easy on the servers. Also, it's not on Steam since EA is fascist.
But, they do make some great games. I got Mass Effect 3 as well. Haven't played it yet, but I'm looking forward to the multiplayer coop on that also.
Really, I loves coop shooters. Wish there were more.