The answer to the mystery that was driving Baldur's Gate is basically the setup for Baldur's Gate 2. If that kind of thing is not a big deal to you then by all means start with the sequel. I played BG2 first years ago when it first came out and I didn't know anything about CRPGs, and having played BG since I still appreciate it. It is a very personal story (as opposed to a generic and impersonal one like saving the world from Darkspawn) so naturally this would lead you to be more emotionally invested in your role in BG2 playing it before-hand.

I second Fallout because it's just so much fun and I usually don't like tactical turn based games but the combat is so easy to understand that you usually forget about it being a tactical turn based game.

PS:T. The setting, the world, the characters, the dialog, the quests, the main story, are all so unique, and more importantly so amazing, that this is the pinnacle of CRPGs for story, and in quests in many instances. Combat is extremely few are far in between, though.