Let's see here...
Looking through Steam I see a lot of games I didn't finish, but most of those games are very very bad games I picked up in a sale or humble indie bundle.
There's a few, maybe 6 or 7 of them that might be decent that I ended up deleting to make space for more interesting ones. Among those is, unsurprisingly enough, every Hitman game available on Steam. I tried to play Codename 47 and gave up because it seems to suffer from Morrowind syndrome(directions are vague and poorly explained at best, terrible controls and combat, etc.) and leaves you to throw yourself at a problem 1000 times until you accidentally stumble across the right method to do it, then you have to throw yourself at the right method 100 more times to get the stars to align and actually succeed.
I did finally just skip it and move on to Blood Money and it's a lot better, haven't gotten around to finishing it yet though.