Summary
I mean, this is a really REALLY good game!
The Good
In Ultima Online, you can do just about anything. People have even built whole towns run entirely by PC's! (player characters, not personal computers) I myself have held auctions, organized hunting parties, killed some really evil and powerful monsters and a lot more than that, just with one character. There is huge amount of possible professions to choose from, too.
The Bad
If you wanna create a character, buy some weapons, leave the town and kill a few ogres, don't buy this game. Building up your character takes time. And then there's the thing about paying 10 bucks a month, but that's definitely worth it.
The Bottom Line
I personally believe that Ultima Online: Renaissance is quite literally the best game ever made. That is, until Ultima Online: Third Dawn hits the shelves. You create a character by choosing from a number of character templates (or creating your own template), designing their looks and then send them out into a world full of interesting players, NPC's and (my personal favorite,) monsters. A real must-have.