First of all i have to tell i have this game also on original disc, i bought it also here cause i find easier and faster to install it when i wanna spend couple of days on it.
I played, or at last "tryed" all 5 chapters.
This one in my opinion is the best HOMM chapter, froget IV and V that are not the same game (and are not on GOG btw), and HOMM II is nearly same as this one but with older graphic.
This game is the classic turn based fantasy where you need to explore, find artifacts, level up and improve your heroes, build structures to develop new armies etc.
This is the best one i played until now, also there is a random map generator and a solid editor that basically add infinite longevity to this game.
If you like turn based games this is a must.