LePeureux: Okay the obvious answer would be the first game. But are they all equally good? Should X earlier game be skipped for X reason? I really liked games like BG /fallout/avernum series. Over the years ive built a pretty high tolerance level for dated games (picked up the elder scrolls 1 not too long ago and lovd it so much when it didnt crash bc of compatibility)
I like games with good combat on top of the story, I actually never finished ps: torment because of that. The graphics are not a factor to me.
Ultima 2 is generally considered the worst of the early games, so skip that one. The rest are worth trying, however.
Ultima 1 is rather simple, and it does have a mandatory arcade-style minigame. (One unusual characteristic of this game is that there is no max HP stat; you earn hit points much the way you earn something like gold. Also, the best way to get HP early is to go into a dungeon, kill some enemies, and then leave the dungeon.)
Ultima 3 introduced the party system, and has the most interesting class system in the series.
Ultima 4 is where the series developed its own identity. You have the modern Britannia world map (also used in 5, 6, and 7), the 8 virtues, and it is here that the series starts differentiating itself from other RPG series. (Unfortunately, it's also the game that introduced the need for reagents to cast spells.)
Ultima 5 can be seen as a logical successor to Ultima 4.
Ultima 6 switches to a continuous world (instead of having towns and combat on separate maps), and is also the first game in the series to keep track of things like which townspeople you've killed.
Ultima 7 switches to real-time combat, and the transition did not go well; if you are looking for combat, play the earlier games in the series instead.