I have this nasty habit of having trouble starting games, and trouble finishing them. It doesn't happen too often, but when it does, its brutal. None of the reasons are because the games are boring, far from it. I just...can't explain it.
There were many games where I get maybe a couple of hours out of it, but just stop right when it opens up. I can take me multiple restarts of the game before I finally get into the grove of actually playing it. For games like L.A. Noire, Dark Cloud, and Mass Effect 1, I always reached a point before stopping, and just never going back. Good thing for Dark Cloud and ME1, I eventually managed to go back (took about 6 tries in Dark Cloud's case) and beat both games, loving them a lot. Sadly, still have to go back to L.A. Noire.
The other problem is just finishing games. Technically, its not even about losing interet. I will usually reach a point in the game, where I may get stuck on a section that is particularly annoying, or I may have just gotten through one such area. I will stop, and not go back to that game for a very long time. It doesn't even have to be that annoying of a section, could be something like, "Man those enemies just wouldn't die" or "Man, gonna have to level up my characters". If I can't past a section, instead of stopping to cool off and go back later, I just cool off...but never go back. Current games like Castlevania, Devil Survivor, Dragon Quest 8, Lost Odyssey, and Catherine have been some unfortunate casualties.
The worst part is that I can pretty easily get back into a game (unless of course I have gotten pretty far but am completely lost as to what is going on, in which case I may restart it), all it takes is a simple grabbing of the game case. I just...don't do it. I know I will eventually, and I have actually been trying to remedy this over the years (to good success actually. No longer takes me like 2+ years to get back to a game).
My dad is the same way, so maybe I get it from him. =/
Edit: Oh, and I can NEVER be a bad guy in a game that is all about moral choice. Its literally impossible for me. I love to go on youtube and see some of the alternate choices, and usually I am pretty disgusted in what can happen. Like Mass Effect 3, pure renegade? Jesus, you are pretty much a complete monster in that game.