Definitely second Master of Magic and Darklands, both are fabulous. Darklands in particular was a huge influence on similarly open-ended games which came later, particularly the later Elder Scrolls games. Master of Magic is basically Civilization II meets Magic: The Gathering with the latter's serial numbers filed off; the influence is unmistakable though. Microprose had the Magic license at the time, so it's entirely possible the game may have started out with the Magic branding and they decided to separate it midway through development.
I feel like Might and Magic is metaphorically the Final Fantasy of PC first-person dungeon crawlers: the gameplay, even from the first title, is significantly more casual and less difficult than its contemporary competitors, and the game has more of a narrative focus than Wizardry or Bard's Tale ever did (probably rivaled by the AD&D Gold Box games though). The analogy holds in one other way too; Might and Magic revels in referencing Star Trek throughout the franchise in much the same way FF does Star Wars. Anyway, all five DOS Might and Magic games are pretty great, although the first is really rough around the edges nowadays. I still think it's worth playing, but the series did get better with each successive entry at least through World of Xeen, and M&M6/7 (for Win 9x) are still good games as well. (Disclaimer: M&M1 was the first RPG I ever played, so I may be biased.)
Speaking of Ultima IV, it's also an excellent game, for all that the DOS port is one of the worse incarnations of it. DOS also offers Wizardry 1-7 for RPGs; however, the DOS ports of 1-5 are awful and I can't recommend playing those in good conscience. (Even on the better platforms, they are seriously dated games. If you really want to play Wizardry 1-3 or 5, play the SNES ports; if you really want to play Wizardry 4, play on the Apple II version.) 6 and 7 are DOS native though. Neither are bad, although I think the contemporary Might and Magic entries are far superior.
Similarly, while Bard's Tale is considered a classic, the DOS ports of the series are the worst versions, avoid them.
The Magic Candle is an oft-forgotten classic DOS RPG too which is pretty good and does some things that were fairly ambitious for the time. Give it a whirl.