Games you have up half way through?
Prince of Percia (Open ended world became boring too quickly)
Call of Juarez: Bound for Blood ( Excellent game but up to a certain point it was enough)
Final Fantasy 12 (Incredible production values, watered down story with no direction)
Brutal Legend ( Great writing, presentation, voice acting, bland gameplay)
Infinite Undiscovery (Just too long. Great Story though)
Fallout 3 (Spend 100+ hours on sidequests and exploring but only did the first two chapters in the main story)
Tiger Woods '10 ( Stopped playing it my personal stats started to go down ;_;)
That's all I can think of. Any games where you just stopped caring?