This is the kind of game that gets you the best of shooter and the best of storytelling.
The game is good. Sometimes to hard so I recommend to play it on easy if you do not want to spend hours on it.
I think that the perfect length is about 10-12 hours. This game last that but maybe I left a lot of things uncovered.
This game has to ending both sad but the good one is the one you want to get, right? I gor the bad one. I order to get the good one, I do recommend no to use the knife and avoiding killing only if it necessary. With the ending I got I feel that I put 12 hours in this game to be sad at the end... crazy.
I enjoyed more the last part than the first part because of the depth of the story. If you have played Metro before you have to try this. The best Metro so far.