Take Baldur's Gate man !
IWD is more combat oriented. Well, scrap that. It is simple hack and slash with some dialogues that have very small impact on anything.
BG is much more then that. There are plenty of very challenging battles, but also interesting characters, scenarios, side-quests, dialogues... Also, it can be further expanded with very good unofficial mods. Ultimately, with application of "Big Picture" BG becomes equal in content to biggest crpgs available.
Edit :
Googled "Big Picture" for you.

http://blog.fileplanet.com/2011/06/20/monday-mod-baldurs-gate-big-world-project/
http://www.shsforums.net/index.php?app=downloads&showfile=963