I think if it had the free roaming, it WOULD pretty much be stalker. It is made by some of the original stalker dev team after all. I'm glad it's a pretty linear game. If you want to roam and spend days exploring, then you have stalker for that.
I'm currently playing through metro now and I'm enjoying it. Just picked up the 6 slot shotgun and AK-47. My only complaint is that the AI are a bit too sharp and detect you too easily, and the gunfights could do with that extra bit of polish. I sank 7 shotgun rounds into an enemy from about 3 meters and he still didn't drop. Other times, you can kill someone with 3 bullets from your standard revolver.
Apart from that, it's a great game.