Ok, I'll start with RPGs that I actually played that reviewers praised while most RPGCodexers acknowledge were bad:
Ultima IX: I was a huge Origin fanboy, but what a pile of crap this was. This game changed my opinion of the company. I quit after I saw what the developers did to poor Iolo.
Neverwinter Nights 2, Mask of the Betrayer: I really am angry at myself for wasting my time with NWN 1 and its expansions, then NWN 2. I guess I liked some of the fan mods and was hoping for a return of the Planescape and Baldur's Gate feel that I really loved. I know a lot of people praise Mask of the Betrayer, and I wanted to like it, but the horrible NWN engine could not make this game any fun, although I did ironically enjoy the story more than the previous NWN games, and thought the shadow land was well done. I quit shortly after that mission. I think I was just worn out of the engine at this point. Unlike in the previous Mask of the Betrayer games, I did like most of my fellow party members. Except Gannayev of Dreams. God, I wanted to punch him in his face. I didn't try the later mods, and they might have been good, but I don't ever want to see that game engine again.
Final Fantasy XII: I play a little whiny girlie-man while the two other male party members are supporting characters? FAIL! I gave up 3/4s into the game. If I ever buy another Final Fantasy game, it will probably be that recent reworking of Final Fantasy Tactics: War of the Lions.
Dragon Age Origins: I was already skeptical of Bioware after NWNs 1 and 2. I finally learned after Dragon Age Origins. I felt they tried to hard to be edgy and a lot of comments and scenes seemed to be tacked on. Like the cleric who liked to bone and the uber-goth mage chick. The gameplay was horrible, the towns were not interactive and nothing in the world made sense. I was almost ready to quit when I found some bandits sitting on the edge of one of the towns. I dragged them into the town, thinking that the guards would help me kill them, but instead they chased me around while the townsfolk lacked any reaction to a running battle in the streets. I quit when I saw the typical savage werewolves and the Lord of the Rings Treebeard knock-off. I think I was about a third of the way through.
This is a list of games that many Codexers liked, that I could not finish.
Dungeon Master and Eye of the Beholder: I actually prefer turn-based games. These have a great reputation, but they are too much of a hybrid of action and pen and paper party-based play. I'm currently am playing the Might and Magic series starting at number one, and the first Ultima Underworld and am having a blast. It has the same perspective as these games, but allows me to take my time (MM1), or has me only focus on one character (UW1). I did finish and enjoy the similar Dungeon Hack, but probably because it felt like a rogue-like.
Ultima VI: Again, I love the Ultima series (except 9). But I just couldn't get into Ultima 6. I hate the cheesy grins on the faces of your rescuers during the opening animation, the interface to pick up and use items, and the color scheme that makes it difficult to understand what I'm looking at. Sorry, but I can't get more than a few hours into this before giving up.
ADOM : I keep trying to play a troll, which means I keep starving to death. So I can't finish it, but that's mostly self-inflicted. I will finish you one day, ADOM. Oh yes... I will.
The Temple of Elemental Evil: It's really my fault. When I play a game, I want to kill everything, so when I got to the elemental rooms I wouldn't just grab the items and run. I took the battles as a challenge, and died about 20 times. Finally, I uninstalled the game in frustration. I liked the game until that point, and was nearly done, but I doubt I'll ever come back to it.
Elder Scrolls Arena and Elder Scrolls Daggerfall: The combat is just too choppy for me. I tried to get into these games, but swinging my sword around never felt natural in these two. I've retried them several times but quit after a few hours.
The Bard's Tale: It's just a hack and slash grind leveler. At least Might and Magic 1 and Wizardry have better puzzles. I'm sorry, but this game is overrated.
Curse of the Azure Bonds: I loved the Pool of Radiance game, and am having a blast doing my Let's Play series on the FRUA fan mods. But I just can't get into Curse of the Azure Bonds once I leave the city and go through the overland map. Something about it is just not clicking for me. I think what is dragging me down is the overland map lacks the exploration of Pool of Radiance, and that the high-level play just doesn't seem as fun for me as Dungeons and Dragons combat from levels 1-7.
Betrayal at Krondor: The turn-based combat looks right up my alley, but I can't get passed the horrible real-life portraits of people in bad make-up. Maybe I'll come back to this, but it might be some years, with all the Might and Magic games, half the Gold Box games, FRUA fan mods, Albion, Ultima clones like Excelsior and Ultizurk, Realms of Arkania series, Magic Candle Series, Wasteland 1, and Dark Heart of Uukrul still in my queue. God, I love Abandonware and DOSBox.