A Great Sequel!
The game took the elements of the original Baldur's Gate and made them better. The AI was improved so that when one member of your party is going to pick up treasure, other members will move out of his way. The 800x600 graphic size was a welcome improvement (though you can still play 640x480 if you wish). The ability to make notes in the journal was great for tracking important things like a specific place to return when a quest was completed. Also, now your party gets XP for doing things like picking locks and disarming traps. Conversations with NPCs are better done.
What I didn't like was the repetitive music. Don't get me wrong, the music sounds great. It's just that after a while I was sick of hearing it (but I'm always like that). Also it seems that the number of quests gets to be a bit much. Granted doing all these things build experience points but most of them have nothing to do with the main storyline. So at times I would feel like "Ugh! Another tedious quest to do but hey, it will gain me XP and maybe a higher reputation).
The Bottom Line
Basically this game picks up where Baldur's Gate ended and goes from there. There are all kinds of new monsters to challenge your party as you become more powerful. Plenty of new items, spells, etc. in this game. If you like RPG games or D&D, you'll really enjoy BG2.