Oh God, people are going to hate me because of my choices, I just know it.
Best?
Baldurs Gate 2 - I never could get into 1, but this is the RPG that got me into this whole series, the cast was amazing, the story was well written, the gameplay was tactical, and made you think, and everything new was just so shiny and exciting.
Fallout 1-2 - The amount of choice they really gave you was amazing, the story meshed well, and it drew you in, the first game wasn't much, but this was a long time ago, and for its time, it was great.
Planescape : Torment - If I need to say more, you obviously are not a RPG player.
Oblivion/Fallout 3 - Basically love them for the same reason, HUGE open worlds, tons to explore, plenty of mod capabilities, your character never really ends in these worlds, and they feel rich, and full of life, you really feel like a citizen of Cyrodil or DC when you play these games, although the endings of both games left me slightly disappointed, but such is open ended RPGs I suppose.
Vampires the Masquerade : Bloodlines - Normally I hate Vampire games, this one proved to be one of the best RPGs I have ever played however, characters I remember even now, interesting story, interesting gameplay mechanics, it was a great game, even with all its bugs.
KotOR 1/2 - I hate Star Wars, with a passion, so the fact I enjoy these games so much is somewhat of a surprise, I just like the characters in both of them, how the games play, the way the story unfolds, and how the characters interact, it was one of my first Bioware games after the long passing since BG2.
Jade Empire - Gameplay kinda sucked tbh, and there was way to many confusing features in it, but it was all made up for in the storyline, a friend told me not to do any background research into the game before I played, so I went in with no idea what would happen, and the surprises that game throws at you have yet to be equaled.
NwN 2 - Crossroads Keep, really, I don't need to say more but I will. The actual game itself wasn't that great, it was basically NwN p2, and I never really liked the first, due to the lack of a real overarching storyline, however it made up for this, and got on my list of greats due to Crossroads Keep, it added so much to the immersiveness, made me really feel like it was my keep, and my responsibility, and it was nice to see my actions change things, even minor stuff, and for a ton of cash. I'd LOVE to see something like this added to a Bioware game, as I expect they could do SO much with the idea.
Worst
The Witcher - It started out good, and the background story was well written, but playing the game felt like more of a chore then an actual game, I had to learn all these silly little things, just so I could so something, I had to put in hours of working farming for something, just so I could be effective, fighting felt out of place, it was just a mess gameplaywise, which is a shame, because after reading the various wikis as to how the story went, it had a TON of potential.
Mass Effect - No offense Bioware, but this first game was to me not that exciting, the "epic" storyline I remember less of then the story of Doom 3, compared to other Bioware games, the characters were forgettable, and the gameplay was mediocre at best, add into this the bad inventory management, itemization, and silly secondary quest stuff rather then actual interesting, well built quests, and I tag this under a game that could have been great.
NwN - I had a friend who would constantly tell me about how great this game was, and how I, our little groups RPG lover would love it forever and ever, so I went and got it, and was fairly unimpressed, the combat was decent, the story line was decent, but the heart of the game was more about level gaining, and item finding then the actual storyline, and it just made the game feel kinda flat.