Baldur's Gate is definitely awesome, though I feel the first game has aged somewhat poorly. With that said, when you add the expansion pack you get one of the best dungeons ever made imo: Durlag's tower, whether you're trying to climb it or descend it, I freaking love durlag's tower
Want to do Durlag's tower in hard mode like I did? Get a party of 6 people, all of them level 2-3 and completely explore that thing, I guarantee you by the time you're done, you'll have a huge sense of accomplishment and the party should be near the max level