Backlog vs Games-I-Don't-Enjoy

In general I try to do some minimal research and only play stuff that I know I will enjoy. Some stuff fall through the cracks though. Like games with achievements that seriously take the piss on how much I'm willing to grind - for example Mugen Souls is a game that I like but it's currently "on hold" until I feel bored enough to do the 200 hour grind needed for the final 2 achievements and Killer is Dead was... kinda disappointing, so I decided that I didn't wanna do the significantly less grindy but still somewhat annoying remaining achievements in it.
On the other hand, I have 100%-ed games that I didn't like because I thought that they were waaay too easy to not 100%. The Binding of Isaac and King's Bounty: Warriors of the North come to mind in that category.

There are also games in my Library that I will never play, mostly from old bundles when bad games were merely "crap" rather than "so terrible you should feel embarrassed to even own it". I mostly ignore their existence and never run them so they wouldn't count for my achievements total. :D

You only have a limited amount of time on this planet.
Do what you enjoy doing, that counts for everything. Work, games, friends, movies etc :).
If you don't enjoy playing a game, stop playing it and pick another one.
If you don't like the movie you are watching turn it off and watch something else.
Do what makes you happy :)

If it's OCD, maybe change the goal. Instead of trying for 100% completion, set a goal for how many games you can try that you don't like and can banish into a "no fun" folder. So instead you'll experience joy as your "no fun" folder grows! ;-)

I agree everyone that there is no point in wasting your time on something if its not fun.
I definitely will finish the game if I like it. But I love getting achievements.
Thats whats fun for me. Even if im not much into the game, when I have time or Im just bored or dont have the mood to play any perticular game, I just go and get some random achievements in some random games I would usually play just for fun.

In fact, i don't know. I've tried and played through many games, but it's only since i bought and won games on Steam that i fond myself letting some of them die silentlyin the dark without being 100%ed.
I'd tend to say "Yes, play it until the end, you never know what you get out of it" because that's my philosophy for books, and as such, i always finish books i start. But games are not the same. Even if narratives can get more interesting at the end of the game, the gameplay stays exactly the same 99% percent of the time, so you don't like how the game plays right away, it's really hard to force yourself until the end, knowing you'd probably see nothing more than you've already seen.