Perhaps the most unique RPG ever created, Ultima is not about defeating some great evil. Rather, it is a tale of self improvement and discipline, having the player unite the eight clans of Britannia and conform to each of their guiding virtues in order to serve as a guiding example to all the people of the land. In part inspired by the negative reception to the more, erm, "devilish" aspects of the earlier games, as well as culling ideas from numerous world religions and even the Wizard of Oz (yes, really), the three Principles and eight Virtues served as a building block for many subsequent storylines in the series.
This also marks a major turning point for the Ultima series' design; the world of Sosaria (now rechristened "Britannia") took on a more static design and feel, with its world's layout remaining relatively constant throughout the rest of the franchise. The game also took a much heavier emphasis on the storytelling aspect, sporting much more elaborate characters and dialog and utilizing a keyword system that the player would have to explore in great depth in order to gather clues from. It also featured a much more in-depth magic system (featuring the first use of "reagents" as a component) and a larger party size, enabling up to eight characters to be in the party at a time (in fact, having all eight characters present at the end of the final dungeon is a requirement to completing the game).
It is also the only Ultima game to be released as freeware, and can be downloaded from numerous sites at no charge.
My class was selected by putting my IRC channel to the virtue chest; they favored Sacrifice, so I begin the game as a Tinker in Minoc. Tinkers are relatively strong fighters (being able to equip up to Plate Mail and Magic Bows) but are the worst magic-using class overall, only getting MP equal to 0.5x their Intelligence stat. Still, they do better there than Fighters or Shepherds, who cannot use any magic...
Download the game for free at GOG.com (comes in a pre-configured DOSBox package)
Scanned copies of the box, manual and cloth map can also be downloaded at no charge from GOG.com.
You can also grab a patch at this site to upgrade the visuals and music.