Should I buy this game?

[Arvuti]

For the info you gave, I suggest you to buy Penumbra collection. (I personally liked them more than Amnesia)

...and in the end, if you end up liking the game, you get more gameplay from the collection (three games) than you get in Amnesia (single game).

It took me five hours to complete both penumbra overture and black plague

for amnesia it took like little less than nine hours.