Outside the trilogy of trilogies there are five other games that bear the Ultima name, though not all of them are even set in the Ultima world. The two Underworld games are.
Chronologically, they come between Ultima VI and Ultima VII. Both were released in 1992 and are dungeon crawlers featuring a first person perspective and real-time combat.
I bought the games as a well-made 1996 re-release on a single CD. I played the first game a bit, found it not bad but not too fascinating either. It sure looks better than most contemporary first-person RPGs, especially Betrayal at Krondor.
It is a little appreciated fact that these two games, or rather their engine, which was used in System Shock too, were the first ones that were truly 3D. Games like Wolfenstein 3D or Doom were what is often called 2.5D: they still used two-dimensional maps and could not have rooms above rooms. The next full 3D engines developed were Bethesda's Xngine, used in Terminator Future Shock and Daggerfall, the engine used in Descent, and the Quake engine.
Among the games that support Roland but not General MIDI, the Ultima Underworld games have some of the highest system requirements, requiring both a 386 and extended memory. Most of the others were content with a 286 and 640k (or even less) RAM.
Ultima Underworld's strong point is its plot. Compared to most modern offerings it is far superior. The game is superbly balanced. The puzzles can be hard, but there are clues to all of them. Listen very carefully to everything the non player characters have to say. Talk to them more then once. Always perform the sub quests and erands they wish. Always be honest, polite and don't kill anything that does not attack you first.
Ultima Underworld was one of the first ever 3D first perspective games to be made, using a similar engine to Wolfenstein 3D or Doom except it was developed by and was made by Warren Spector of Looking Glass Technologies; Looking Glass was known as Blue Sky Productions then. It was based on the original Ultima series, and was set in between Ultima VI - VII in the Ultima universe.
Believe it or not I still prefer UW1. UW1 was ground breaking, whilst UW2 was more of the same. I found some of the worlds in UW2 such as the Ethereal Void a little boring as well. But that is only a minor complaint about an otherwise great game.
