Baldur's Gate II is easily the best RPG I`ve ever played.
The story is gripping, with many unexpected twists. You have a number of companions to choose from for your party, and each is unique and has an interesting side quest. You actually get to choose how to do your quests, unlike many other RPGs where your only choice is to either do the quest or say 'no' and post-pone it until you're ready.
There are a great number of different weapons to use. My only gripe with the weapons is that there are too many magical weapons (especially compared to the first game.) The magic is excellent; there are a great many spells and most are unique. There is also a huge variety of enemies to face.
Overall this is an amazing game with little to no flaws. If you love RPGs with great plots, this is a game you'll enjoy.