Ultima Online isn't the grandaddy you think it is. In fact, it was predated by one Meridian59. Often considered the first MMO (at least in terms of how we now define the genre), and thus progenitor of all the Warcraft template that so many of the last half-decade of MMOs is built around, Meridian 59 is an essential artifact for gaming historians. It’s also (apparently) really very interesting even by today’s standards. Combine that with the fact it recently went free to play after 14 years and you have a really bloody good reason to indulge in a spot of gaming archeology.
Given the now rather unfortunately-named developer Near Death gave up the ghost in January and the game’s currently running on a non-profit model, it might not be around for long, so look at it and support it while you still can. You can download the client here, but until the current overlords build a new account management system, you’ll need to email them with your desired username and password to create a free sub.
To get a rather good sense of what Meridian59 is and how it works, I can recommend reading both Eurogamer's recent retrospective and the fan-run Reference site. Had I more time, I'd love to do a Worst Ninja-style nose at the game.
Speaking of which, I wish Ultima Online would go free. It's a fascinating world as it is, but with a surge of population it would be amazing.