Keep in mind that I'd probably have more JPRGs on the list, but I tend to wind up spending hours on them, going off to something else, then get reluctant to go back because I have no idea what the hell I was doing.
1) Baldur's Gate 2:
IMO, the best D&D game ever made. Probably the best example of western developed RPGs to date. Even with your character's background and story set for you, they still managed to give you a great deal of customization as to how you made your character and played the game. A lot of joinable NPCs with their own personalities, conflicts, and storylines. It had amazing graphics for the time, and ones that still don't look bad even today.
2) Fallout 2:
If BG2 is Bioware's best, then Fallout 2 is Black Isle Studios' best. How you play the entire game is up to you - combat, charisma, science, and even pacifism are all viable options. Your stats affect the game, and not just in combat - like I pointed out elsewhere, a low Intelligence character will have serious problems completing the game. It's an open world game at it's best, and has well written dialogue to boot. My only gripe is that they work in a little too many pop culture references - though they're all random encounters, and one area in particular. New Reno is a huge, quest-laden area of the game, and while I feel it's very well done..it just doesn't feel very Fallout-y.
3) Planescape: Torment:
Another great BIS game. It's another D&D license game, but it's about as far from Baldur's Gate as you can go. It ditches the traditional style fantasy setting for something entirely different, and while combat is an option, the game is very story/dialog driven. You can get through most of the encounters or quests by dialog alone, and it avoids the "good choice, neutral choice, bad choice" trap that so many games with a morality system fall into.
4 & 5) Fallout 1, Baldur's Gate 1: Take the opinion from the above games, and reduce them just a bit. BG1 is playable on the BG2 engine, which fixes the gameplay issues the original release of BG1 had.
6) The Elder Scrolls III: Morrowind (and expansions): I love Oblivion, with some of the refinements it provides, but it can't really beat it's predecessor. A fantasy game with an unusual setting, plenty of factions, open world gameplay style, any number of ways to play, and a well written story. When you consider the thousands of mods available, the game is practically endless.
7) Darklands.
An old (1992) game set in the Holy Roman Empire during the 15th century. Extensive character creation, a lot of locations to visit, a location-based infamy system, an open world, character aging, real-time combat, and a ton of other things. A little buggy, but how many games of this scope aren't?
8] Mass Effect
I don't think it's quite the best thing Bioware has done, but a good Bioware game is better than a lot of other developer's "great" games. It's a mishmash of Knights of the Old Republic and Star Control II, and it really works.
9) Knights of the Old Republic
Star Wars + RPG done right. I think the second game is better gameplay wise, but Lucasarts being dicks about it and having Obsidian release the game incomplete really, really hurt it.
10) Grandia 2
Probably my favorite JRPG, and one of the few I've actually finished. I haven't played it in years, but I still love the soundtrack.
Honorable mentions to Oblivion, Fallout 3, and Jade Empire.
