Oooh! I remembered another one: Fable. While it may not be as openended and free as was implied it's still great fun and has better graphics than the games I mentioned previously.

Will try to comment if I remember any other rpgs I think are worth playing.

Well, since you name BG, BG 2 and Icewind dale you might want to play planescape torment and icewind dale 2 if you don't mind the outdated graphics. Also if you liked oblivion you should play Morrowind. Someone also suggested titan quest, if you're into hack and shlash rpgs sacred is great fun (that game is friggin huge!)

That's about all I can think of... excluding games that have already been mentioned.