This game was the first "modern day MMO". It was the best then and it is still the best now. Although the player base may have shrunk a bit over the years. It still holds the #1 position for game that every other MMO tries to replicate.
The fact that after 20 years the player base is still pretty big on official servers shows the staying power of Ultima Online.
If your ever looking for a sandbox game that doesn't hold your hand, hardcore PvP and great friendly players, PLUS some of the oldest and most established gaming guilds to interact with. You should come by Ultima Online first and check it out. There is a trial too, if you arn't quite ready to commit right off the bat.
