6. Gears of War 3
Gears of War is the immensely popular shooter series developed exclusively for Xbox 360, and its notorious for its extreme difficulty and aptly named achievements (Seriously...). 100% here isnt just in attaining full completion of the main game; youll also have to dedicate a fairly sizeable chunk of time to attaining the Seriously 3.0 achievement online, which, I promise you, will eat your life for breakfast.
Why Youll Never 100% It: The Seriously 3.0 achievement requires you to rank up to Level 100, and earn 65 onyx medals. Sounds easy enough right? Wrong. Just one of the Onyx medals, Vengeful, requires you to execute an online player who has killed you 5 times in a row 100 times. This alone could take 50 hours or more of online play, and thats just one medal out of the 65. 100%ing GoW 3 means committing to this achievement for at least the next 6 months to a year of your life and making collecting these
ONYX MEDALS one of your top priorities in life. Yeah, I wouldnt bother either.