I quite enjoyed it when it first came out. It had some really silly problems with it. I left it on my HDD for quite some time after I stopped playing it and I never saw any updates, maybe there are some now.
It has auto aim, yes, even with a mouse. You can't join games are in session. The match making used to take quite some time to find a game, and if it did then there was a chance of a DC.
Playing the game it is quite difficult. It'll only take a few bullets to kill an enemy so you need cat like reflexes when you are in combat. The X Ray goggles add a nice touch, it's completely pointless camping everyone can see you.
For gun nuts, everything is customise able, from the barrel to the stock, I think there's 5 areas of the gun you can change, I don't remember exactly.
My opinion is based on when the game first came out. They may have updated it by now and fixed the various issues.