Played HOMM2 quite a bit in college, along with MOO2 and Civ2.
Clearly it was the golden age of games with a 2 in them!
But anyway, HOMM2 was quite fun. You (usually) start out with a weakling hero and a feeble base-building of some sort. You scour the landscape for resources with which to build up your base, so you can recruit more creatures to fight at your side. You can also meet creatures on the map who will either fight you or, sometimes, join you.
There are magic geegaws you can find, artifacts you can search for, etc. Your hero gains XP and levels up much like in D&D. Some heroes can cast spells, again taken from D&D.
Eventually you confront the enemy hero and defeat him. Lather, rinse, repeat.