Basically what everybody's saying is that games should be shorter because you don't complete them. You know what, that's either yours or the development teams fault.
We're gamers and we buy too many games, most of these games don't really appeal to us. But we buy them because we know they're supposed to be good. Basically you're not completing games because they don’t give you enough variety in game play, don't have a good storyline or don't even appeal to you.
The length is just an easy excuse, those are the real reasons you don't complete them.