I plead guilty to mentioning The Magic Candle series. They remain good, but visually very dated: icon-based, no animation, no music, limited (but interesting) dialog. I do recommend them, but only to people who enjoy that kind of thing. They can be downloaded without any legal problems (being abandonware) from
Home of the Underdogs.
You might also want to see about
Exult. It's an engine that allows you to run Ultima VIIa and b, with their addons, under WinXP. Of course, you already have to possess Ultima VII to use it, but the new engine actually improves the old graphics, and adds a few new features, too.
Ultima V Lazarus uses a different approach: it incorporates all of Ultima V's gameplay into a mod in Dungeon Siege I. So you don't need Ultima V to play it, but you do require Dungeon Siege I. It is very faithful to the original, and an excellent transfer.
Consider buying Might and Magic VIII. While it feels a bit rushed, a lot of it is excellent. Excellent, too, is Divine Divinity, a game that recaptures some of the character of the Ultima games. And while you're at Home of the Underdogs, be sure to download Betrayal at Krondor. Excellent 1st person, turn-based RPG, the first in 3D, too.