Picked it up on sale from Steam over the weekend. Really terrific atmosphere, digging the story and setting, and the gunplay is alright. I'm not too keen on the sections involving human bad guys, but the parts in the tunnels with the mutants and other little surprises are absolutely awesome.
There are a few irritating bugs though. I'm out of filters, so I can't take off the gas mask, and the damn thing just refuses to break, so it's a little irritating looking at the world through a half-shattered visor.
The stealth segments would be really great if there was some grey area between the human AI being oblivious to your presence and every enemy knowing exactly where you are at all times. They put in all those cool elements like knocking over objects, broken glass, and sound traps to give away your position, so going the extra mile to add the guards searching for you would have really enhanced those parts of the game.
Glad to hear they're doing a sequel. Hopefully this one is doing well so they can afford that extra polish on the bugs and AI to make the next one really shine.