Re: Games started but never beaten.
I'll stick to games I currently own.
Darksiders - Got bored about 5-10 hours in, movement in particular was pathertically slow.
Bulletstorm - Got bored of this very quickly, dialogue sounds lik it was written by a 12 year old.
Halo Reach - Turned me off the whole franchise, huge disappointment.
Pure - Very repetitive.
A few Zeldas (Majora's mask, Skyward Sword, Windwaker etc) - Seems a very easy series to give up on for a bit (have finished LttP, TP and OoT)
Tony Hawk's Pro Skater 4 - Convinced it's not actually possible.
Pokemon - I've done the league etc but I've never caught 'em all.