Heroes of Might & Magic IV is pretty much an RPG/Strategy hybrid (much heavier on RPG elements than earlier installments), and had more depth in terms of character building than almost all RPGs I saw. I could develop a hero to scout the area, to help me with management, to give boosts to my troops, or to physically assault enemies; and there were 5 schools of magic, much harder to master than in previous entries and way more rewarding. I could do way more insane things on the battlefield than before with the bigger variety of spells and the ability to choose between an additional hero or an additional unit. I could blend any group of five of those nine sets of skills as I saw fit; each offered unique advantages, and their combinations gave me a specialization (which could also dramatically change the proficiency of a character on the battlefield).
The quality of those elements might be more obvious in campaigns made by users, though. The main campaigns were uneven (albeit some were great - especially the Necropolis), and those from the add-ons were abysmal.