From my 62 games I've finished a grand total of... 2.
The bane of having too many games is having too many options. I'll start a game, make some progress, get bored with it or get interested in another game and when I come back to the unfinished game, I'm too far in and too lost to not get killed quickly which makes playing it more frustrating and I'm not too fond of restarting games from scratch.
I've only finished the Witcher 2, which managed to hold my attention till the end and Unreal Tournament 2k4 which I had finished before buying on GOG so even that one shouldn't count. Also, old games are harder than new ones, I'm a working adult who doesn't have the same amount of gaming time I did as a teen nor the drive to take these games to completion. As soon as the going turns into a hassle, I'll uninstall it. Games are for having fun and if I'm no longer having any, I see no reason to finish a game.
I like the feeling of "Yay! I did it!" as much as any guy, but in the end, I know I'm just punching keys on a keyboard.
I want to finish witcher 2 but i have problem with sequals ( I always wnt to finish the previous one first) But witcher is a huge game and taking a lot of breaks of that game since some quests can be very nasty.