played both of these games quite recently. Metro was great, but break it down and its another FPS. A great FPS with an interesting story but still another FPS. Stanely is definitely the better game overall. Probably had less hours of gameplay, but better quality gameplay with a fun and immersing story. (and the reason it took less gameplay time may just be due to the fact that i didn't wnat to stop playing it till everything was completed)
While Metro last light was a great game by itself, with a good story, I found that Metro 2033 had the better story.
Something about the clanky, rough around the edge gameplay made the overall story much better. You were a random pleb living in a desolate bomb shelter that was somehow thrust out in the outside world with only a rusty smg and a knife to your name. Fighting humans was often simply not worth it because the gunplay was just a little bit weird, which somehow reinforced the story that much more. Little touches like broken plates alarming guard also added to the tense, nerve wracking feel of the game.
That said, M:LL's gameplay is miles above 2033, even though the story is a bit weaker.
I should get around to playing stanley's parabol, some day...