So far, I have been surprised how similar it seems conceptually to Age of Wonders, and wonder why MoM fans did not consider AoW a worthy successor?
AoW was different in a number of areas. For starters, its maps were built like HoMM, not like MoM. They were noisy with little things to be found, and cities were not as influenced by their location as MoM cities were.
City building did not have any sort of picture interface that really gave you the 'feeling' that the city was build built. Sure, you had similar building from an "On paper" point of view, but it still 'felt' too dissimilar to be the same.
There was not much in the way of alternate planes. There was an underground, but since map construction worked like HoMM, the underground was very limited when compared to Myrror. The undeground had specific pathways that forced your movement, unlike Myrror which was just as open as the 1st world. It wasn't a "sub-level" and the freedom of movement and potential ability to research into moving between the worlds at will, the myrror world could resurt in some very different tactics. So I'd have to disagree with multiple planes, because AoW doesn't have it. It has "underground" and thats constructed in a way that doesn't let it be a substitute for MoM's system.
The magic seemed to be too heavy on the battle spells, and the non-combat spells were rarly very useful. I mean, "global" spells had to encompass so much, and yet it did not end up with the kind of diversity that MoM seemed to carry. In a way its kind like Megaman weapons... They had the same 'ideas' but it requires a good blance of abilities and cost before you actually *want* to use them.
The wizard was fairly limited in range as well, and so if you basically had two tactics: turtle until you could cast spells in enemy domain, or build a huge army and sweep. You couldn't really rush the spell tree and go in with heavy magic blazing, because you wouldn't be able to cast spells far enough, or your wizard would be at serious risk.
Magic Spheres were not like MoM's tomes. Magic Spheres let you pick your school of magic, or even up to 3 specialties, but that was the depth of it. Magic tomes in MoM influnced not only the magic you cast, but the amount of that magic you could research. There was a tactic for taking only like 1 tome in "life" to gain access to guardian or something like that. This also effected spells you could trade or buy, since if I recall right you could pretty much buy and spell you wanted in AoW if you could find somebody willing to sell it. Spells were directly related to your skills and abilities as well, since it cost tomes to gain "artificier" and such.
Of course this is all opinion. I'd say that most of us agree that AoW did not "FEEL" like MoM. MoM felt like Cizilization with armies and magic. AoW felt like HoMM with economy, diplomacy, and a "main wizard" type character. I'd agree it was close. When I played AoW I kept noting things that were more or less a direct rip from MoM. But the general game-style was too far off to be a sequel.