I try to avoid games that take only few hours to finish. So, in average, games I play tend to take at least week or two to play through.
Mind you, sometimes even I, a veteran of games, make mistakes. Like the other day I bought the Medal of Honour (2010 version for xbox360) and it took only two nights to finish! I mean what a rip off! Never have I played so short a shooter. Even halo games take longer to complete!