A pertinent subject. I found myself in a similar situations some days ago.
I had GTA 4 since it appeared in 2008; was at 55% of the story. Didn't play it for ~1 year. Uninstalled it yesterday.
I had Assassin's Creed 2, almost at the end of the story (I think). Uninstalled it yesterday.
The same happened for Mass Effect 2. Played about 40% of it and uninstalled it.
I played Star Wars Force Unleashed 2, uninstalled it and returned it after a few hours.
I used to love games and always told myself I'll be a gamer even when I grow up. Now that I have grown up, I don't have the patience anymore. Add the repetitiveness of games and glitches, bugs, boring stories, going to work 5 days a week... well, priorities change in time it seems.