I've been gaming for the best part of 25 years now and all that time I have had real trouble with completing games that I get. Probably down to my little problem with ADD (yes adults get it as well) which means that I usually plonk in another game and forget about the first one I was playing.
By the time I finally get back to playing the first game (usually a couple of months later) I will have forgotten how the game plays. But this morning I did manage to complete Prey on the Xbox 360.
Now I know that the game is not a long one to begin with, but that was fine. I enjoyed the game throughout and considered it to have enough unique set pieces to keep me focused on it.
I think I need to go back to the days of my ZX Spectrum where games could be completed in about 30 minutes. Except Spindizzy, that one is just damn impossible.