A game that challenges you to forge your own existence in a world riddled with monsters, brigands and warring factions.
The game is simply limitless and has plenty of replay value. You can choose to go through each faction's questline separately, along with the main story and side-quests, or you can do it all in one. If you choose to do it all in one it's not a problem; there are many other class/race combinations to choose from, and you can even create your own class.
Although this game does have a fair amount of bugs and glitches, it's nothing truly gamebreaking; only minor problems which serve to create a bit of frustration. And true, it doesn't have a real tradeskilling function, but you can still enchant and repair your items, pick herbs and make potions, among other things.
This game is simply a timeless classic in my books, getting better and better with each play through.