This game is quite flexible in terms of character creation, particularly in the area of character classes. In essence, you can multi-class your characters as much as you'd like (keeping in mind that this will cause slower development). It would be possible for you to design a character as a Warrior-Priest-Ranger-Wizard-Thief... if you had the patience for it!
This game has a neat feature that allows you to reset any of the dungeon levels. In essence, you can keep one set of characters playing in the game forever, if you're that patient.
This is known to be the game that had the tactical combat engine that was later tweaked into Pool of Radiance.