Only a handful of games have I ever went full fledge OCD: Dead Space, Bioshock 2, Halo, Halo 2, Halo 3, and Borderlands 2 in regards to Jakobs equipment.
Dead Space I have beaten a told of 29 times, had all the spawns (enemy or otherwise) memorized and could word for word remember all the chats in the game. The last two times I played I went through with only telekinesis and trolled all the enemies using the invisible walls.
Bioshock 2 I have beaten 31 times on all difficulties on the console; 3/4 were using the Drill exclusively. Again had spawns and conversations memorized and whatnot. Wish it was a sandbox like the first Bioshock.
Halo was the first game I ever eagerly dived into the hardest difficulty and actually enjoyed. I have played that game so many times I have long since lost count and developed a photographic memory of the game. Years later when the Anniversary game came out I cranked it up to Legendary and had it beaten in a couple hours.
Halo 2 I screwed around and found all the skulls, the two Scarab guns, spent hours trying to find out what is in the floating box, and located a couple other Easter Eggs in the game. The orbital shot glitch was a pain in the ass to get right. Figuring out how to make a Scorpion spine like a top and bounce around blood Gulch was helluva lot of fun.
Halo 3 and the Invincible Dumpsters was fun. Turning on all the skulls and trying to beat the game; not so much.
The one thing I am consistently OCD about though is keeping my magazine full; even when I am being shot at or have only spent one bullet.