Simply the best RPG ever made!
This game has it all: great plot, magic, awesome graphics, great characters. And the main thing is that you don't have to stick to the main plot, but you are free to go anywhere you like, do whatever you like and you can do your quest whenever you're ready.
I loved the idea of the character constantly growing, so it's like you're going through his whole life.
Apart from that, you can do a few extra things, like buying properties, getting married, have sex etc. Things like that make this game more interesting. You can also do a few quests on the side for extra gold.