Dominions_3 has extreme gameplay depth. The huge massive list of spells(many which are different) and huge massive list of units(many with RARE abilities/attacks) opens an enormous amount of strategic gameplay and this doesn't even include the extra gameplay strategy depth from items, dominion preaching, +/- scales chosen, battlefield orders, hidden magic sites, etc., .
The game can be very difficult for beginners... so I advise those trying the demo to first play with only a few opponents on a large map... this will allow you time to actually build, expand and learn the basics. Anyone who has the patience to learn this game will keep it installed for many many years.