As was already stated, this is pretty much civilization in fantasy world, with technical research replaces by arcane arts. Difference between races far surpasses even what Civ4 offers nowadays, the number of buildings in cities and non-magical units is sufficient, everything civilization offers is there.
And there's also a lot more - tactical combat, not terribly deep, but with units abilities, ranged attacks and most importantly spells, it offers enough choice to really change the outcome, heroes with some basic RPG elements and item gathering, ability to influence the world with global enchantments (why not make all killed units rise as zombies under your control or help your ships sail faster with wind mastery) or a number of other ways to influence units and cities on the map or two parallel planes of existence between which your units can travel (and which you both need to conquer).
There are two main things that drag the game down - graphic that was ugly even when the game was released and rather poor AI which would often run units around your undefended cities, clearly not being interested in conquering them. Even with these two though, it's a game no strategy fan should miss especially because of its almost infinite replayability (number of races, five schools of magic and, most importantly - randomly generated maps!). Golden classic of the genre.