For me (and, I guess, not only for me), the Ultima games are the ultimate experience in RPGs. Featuring a great depht in gameplay, and a fantastic blend of story and unfolding things, Ultima games (and especially Ultima V and VII) are true master-pieces of computer gaming.
Ultima 1: The First Age Of Darkness is the first true Ultima game. Ultima 1 appeared on C64 in 1986, which is some time later than the actual Ultima I that got out in 1980, from what I can remember.
The story says that, a long time ago, The Realm has fallen into a dark time; the evil wizard Mondain has cursed the land, and all sorts of unsavory beasts roam the world. You can probably note that we're not talking about The Avatar (which only got into the series in Part IV-Quest Of The Avatar). Your mission is to save the world by slaying Mondain.
The gameplay is notably touched by the fantastic imagination of Richard Garriot. It is by all means admirable how the adventure takes place. The first thing you do is offer your service to Lord British. After that, you get different missions, that eventually lead to you slaying Mondain. In fact, Lord British from the gae is somewhat of a Game Master, and this gives a great depth.
The game has actually got three places where it happens: The Realm (outside world), the cities and the dungeons. The Realm and the cities have the avatar in a tile-based environment, in an overhead view. The dungeons are well evoluated for the time (think that the game is incredible huge, it has epical dimensions, and fitted into a few kilobytes), featuring a (still) tile-based environment, but first-person. Now don't expect a Quake engine or so, but this has an incredible depht, as the dungeons are heavilly populated with giant rats, thiefs, skeletons and other such beens.
The character evolution is realistic (you don't get experience by wandering through The Realm and don't improve magic by fighting with your sword), but fairly restricted to only a few stats. Still, in 1986 on C64, Ultima I has more stats than Diablo II, and it is not skill-based. On the other hand, you can learn some magical tricks. In fact, a good part of the game is based on magic, which can save you many times, and which can get you to solving certain moments of the game.
The game did have some inovations (which, unfortunately, are not adopted today). You have some food which you consume by pointlessly wandering through The Realm. You can also buy a horse, or even a frigate, that enable you to do certain things (you consume less food per square if you travel on horse). In fact, Ultima I is a truly impressive RPG, even nowdays. Having an incredibly absorbing gameplay, and, in fact, quite decent graphics, Ultima I is truly a must-have for any C64 lover, and a potential nights-eater for RPG fans.