Not wanting to sound like an Interplay/Black Isle groupie, you should seriously consider the aforementioned games: Baldur's Gate 2, Fallout 1/2, as well as Icewind Dale and Torment.
It really just depends on your mood and what you feel like playing the next couple weeks.
In a dark, somber mood, feel like everyone's out to get ya? Play Fallout - hell, if you've never played it, play it regardless of mood <img src="/ubbthreads/images/graemlins/delight.gif" alt="" />
In a contemplative, mystery-solving, traditional fantasy mood? Baldur's Gate 2's story will draw you in like few others - and has the content to keep you enthused for quite a while - easily twice the game length of Divine Divinity.
Feel like experimenting with being able to build an entire party to your standards but also want to KILL KILL KILL? Icewind Dale 1 and its two expansions will keep you happy. Story-wise, it is far superior to its sequel that came out last year, but being an Icewind game, it has much more 'hack-n-slash' than, say, BG2. Again, it's a traditional fantasy setting.
And, saving the best for last, Planescape: Torment, now discontinued, the best crpg ever made, period. It's story surpasses even BG2's, in my opinion, and that's saying a lot. Get it on ebay if you can't find a copy in the bargain bin for $10 at your local media store.
