Disciples used to be the big competitor to Heroes of Might and Magic. Where it mostly shines is the graphics. The hand drawn(?) graphics are simply amazing, even compared to the newest HoMM. The reason why D2 was poorer in sales is mostly the gameplay. The combat system is unconventional at best and the fact that one could completly anahilate even high level heroes with a set of magic spells on the worldmap greatly hindered multiplayer matches.
If you buy it, wear a hat. You dont want to lose all your hair for getting your main hero killed mid campaing and having to restart the whole scenario.