In a shameless bid to promote the NEW metro game, ThQ is giving the old one away. Seriously. Go here: http://www.facebook.com/MetroVideoGame I've only played it for about an hour so far but it seems very solid. The theme seems to take after the STALKER games: post apocalyptic Russia, mutants, weird anomalies, that whole bag. A very polished horror/shooter with a heavy emphasis on atmosphere. Again, limited play experience so I can't give a full review, but at the low, low price of free you can afford to try it out and form your own opinions.
It's nice, similar to "Singularity" when it comes to general gameplay (other than the time shenanigans, or rather lack of them) but somewhat more polished.