I do think the thread should be limited to games that actually have an ending, because, eventually, we all tend to quit playing open ended and/or multiplayer games like MMO's, Destiny, TF2, etc. Also rogue-likes, since they are really made to be played infinitely.
I usually make it a point to push through games once I start, but, that said, I have had a few games that I felt were too bad or boring to finish. Some of these are:
Tom Clancy's Ghost Recon: Advance Warfighter, Xbox 360: Just bad. Bad. Bad.
Splinter Cell: Conviction, Xbox 360: Too scripted. Too boring.
Alice: The Madness Returns, PC: Overstayed it's welcome. 20+ hours in, less than halfway and repetitive mechanics.
The big ones for me that are relevant to the thread though:
*The Witcher 2, PC: Gorgeous game. Generally good stability. Loved The Witcher 1. Have played TW2 to between 8 and 20 hours a couple times but always stop. I really have to say that I actively dislike this game. Whereas TW1 had silly combat mechanics, I feel like TW2s are just sloppy. I know a lot of people love it, but it feels floaty and unresponsive compared to what I consider "tight" action games (Souls games) or "fast" action games (DMC, Bayonetta, etc). When one of the games devs feels the need to make a huge mod to "fix" the combat, that says a lot. Also, the potion mechanic in that game is just silly (yes, I understand *why* it was made that way, in response to the books; that doesn't mean I have to agree with it or like it).
I also can't stand the characters and find the story not-particularly compelling. The human/scoi'tael thing doesn't work for me because both sides are consistently monstrous. The characters are bland or just plain jerks and, whereas I could completely get along with Geralt in TW1, since he was a loner and sleeping around was fine, it feels uncomfortable for him to be hitting on/sleeping with everything he meets when the game strongly suggests he has developed some form of relationship with Triss. I realize that he probably doesn't feel that it's that way, but it is certainly suggested that Triss does, so it just comes off as unpleasant to me.
I try to stay pretty far away from GG and the whole sexism thing as well, since I don't consider objectification or "damsel in distress" to be inherently sexist, bad for games, or bad at all. I've very rarely ever seen something in a game that I thought was actually full on sexist, but TW2 was one of the only games that made me feel that way, though it had nothing to do with Geralt's promiscuity or the prevalence of sexuality in the game. Instead, it was the treatment of two female characters in Flotsam. Primarily it was related to the character Ves and the mission to take down the mayor. She was to pose as a prostitute (fine, no biggie) and open the window to let Geralt in. However, we've already gone from the beginning of the game being told that Ves is pretty much a badass secret police agent/soldier and I was wondering why, if she gets the mayor alone does she 1) need Geralt at all, frankly and 2) why, even given that, she would allow herself to be chained to a wall half-naked and potentially abused and raped? It felt very, very contrived and "hey look, a girl is about to be abused, better save her!" I hated that scene. I also thought it was lame the way it was generally suggested Triss was kidnapped. Again, we're told Triss is one of the most powerful enchantresses in the world and while I accept her being kidnapped by the villain character at the time, it seems to have gone off almost completely without a fight, almost like she just fainted at the sight of adversity. The signs or suggestions of any actual struggle on her part were minimal, which seems to defy the character they wanted to paint her as. I didn't care for it.
I've pretty much given up on the Witcher as a series after that, realizing that the story is just not my taste. I still fully respect and support CD Project though. I think they are generally a fantastic company.
*Divinity: Original Sin: I'm a huge fan of RPGs, particularly the top down/semi-isometric story driven ones in the Infinite Engine style. However, I've tried to play D:OS 3 times (once with my wife) and I have never made it past around the two hour mark. I know that a lot of people say that the first 5-10 hours are a real slow burn and the game gets hugely better after leaving the town, but the game starts with such a lack of a hook or real motivation that I feel like I'm just aimlessly wandering around talking to poeple.
One day, I'll decide to push my way through it, but I'm playing Pillars of Eternity at the moment, so I don't know when that will be.