When you think of sequels that deviated from the original game's formula, what games do you think of? Zelda II: The Adventure of Link, Super Mario Bros 2 (USA), and Castlevania II: Simon's Quest, are a few examples that come to mind. One thing those three games have in common with each other and not Heroes IV? They're (largely) the second installments in their franchises, where it's early enough to experiment and not interfere with a formula that worked, which was a huge complaint with Heroes IV that fans had.
Heroes of Might and Magic IV was released on March 28, 2002, and it had a troubled development history, namely from one unavoidable factor: 3DO, the parent company of New World Computing, was undergoing bankruptcy at the time the game was being developed, finally filing Chapter 11 bankruptcy in 2003. This meant that the game was rushed and didn't have the resources to make the game as good as it could have been. As a result of that, I'm more willing to be forgiving of the game's flaws, numerous as they are.
As I said at the end of my thoughts on Heroes III, it would very difficult to surpass the high standards that game had set up for future games, so the developers decided to go with the experimental route with Heroes IV. The problem is that while a lot of the ideas sounded good on paper, they didn't exactly execute well.
The first of the large changes that had been made was rather than having Heroes sit in the back during combat and slinging spells, they are now actually playable units, and the class and skill systems have been completely changed as a result (like in Heroes III, each faction has a might hero and a magic hero). No longer are the heroes' main stats their primary skills and their abilities gained from level-ups their secondary skills: the secondary skills are now prime skills while the secondary skills are extras branching off from them. However, this means that the skills are more or less about improving the hero's combat capabilities rather than improving your creatures or other aspects of combat, and the magic skills are virtually identical to each save for their respective extra skill to help what its supposed to do--seriously, all of the magic primary skills have the main skill that allows the hero to learn the magic school, and secondary skills either give extra spells points and boost magic point recover, increase the effectiveness of the respective magic and then one extra that ties into the magic's theme--which makes all the magic skills mostly identical. As well, your hero's class is determined by the combination of skills that you pick, and classes get an ability based on that, but not only are some of the class skills rather lackluster in comparison to each other (a boost to the Summon Wolf spell compared to reducing the cost of spells by 2, for example), but there's no way to back to a previous class with a better ability if you end up taking another skill down the road (for example, being a range attack boosting Ranger from Combat and Scouting and then getting Order Magic turns you into a Seer with a +2 to uncovering fog of war).
Additionally, while it sounds cool to have heroes in combat, unless you get all the good artifacts and skills, your heroes are going to fall in combat faster than a parachuting elephant--and in my personal experiences, even with all of that they still fell like flies. This is largely because creatures can still stack with each other while heroes cannot, which could easily lead to a stack of 20 Black Dragons tearing down a hero like a paper shredder. Thankfully heroes can be revived free of charge, but that's assuming you can get them back to one of your towns, and if they're defeated by the enemy, they'll be captured and placed into prisons, meaning if you want to get your hero back, you'll have to siege the town they're being kept in.
A hero's army size has been increased beyond seven, which is largely to allow for more than one hero to be in the army--or an entire army made of heroes. Furthermore, a hero isn't always required, meaning you can have an army made up of nothing but creatures you recruit, though they'll be unable to engage a hero in combat, capture mines or other tasks that require a hero.
Factions and town construction have changed as well. The factions have been arranged into a system very reminiscent of Magic the Gathering (something that a lot of people noticed, not just me) in how it handled its elements, with all but one of its factions tied to a specific magic school (Life, Death, Order, Nature, and Chaos, with Might being the exception), and the factions have a kind of "friendly relationship" that allows their mage guilds to have extensions which teach spells from the related magic schools. In a step backwards from Heroes III, the town hall and its upgrades don't give out as much income as they used to (not only are capitols absent, but they only give out 1000 gold per day, which was the standard back in Heroes I and II), and going by how creature dwellings now give out on a daily basis over the week rather than having all of it arrive at the start of the week, it quickly drained my gold supplies to keep my heroes and garrisons supplied with creatures (though that could just be me being a lousy player).
Creatures had several changes that often had me scratching my head. Upgrades were eliminated, neutral creatures were now aligned with the towns though with the exceptions of Nature's elementals they couldn't be recruited in towns, and the creature tiers were knocked down from seven to four. In what I believe was done to try and compensate for this, you had to pick which creature dwelling you built for the specific tier past the first one--once one was built in a town, you weren't able to build the other dwelling in the same town, and if you wanted the other creature as well, you have to build its dwelling in a different town, which does help make different towns of the same type stand out (which was probably the main intention). While it is an interesting idea, it didn't exactly work well because there were some creatures that were favoured over others: the Genie being able to cast useful spells was more favourable than the naga doing no retaliation melee attacks, or White Tigers having better stats over the range attacking Elf, to name a couple of examples.
The campaign mode is kind of lacking too. The setting has been changed after the world of the previous three games got blown up and the survivors managed to escape through a portal into a new world, and the story is about how several of the factions are coping with their new home. Destroying the previous setting that fans grew up with and traveled in for several games feels like a punch in the gut to the fans, since the new setting hardly feels like something that would live up to the example the previous setting had, even if such an event had been foreshadowed in other Might and Magic games. (With The Legend of Zelda: The Wind Waker destroying Hyrule at least matched the theme of the game's story and the Great Sea did feel like it could fit in with the other Zelda settings, but Axeoth doesn't exactly have that.) The problem with the narrative is that all of the stories are standalone and don't connect with each other, which leads to the campaigns mostly being mirror matches against your own faction (the Nature campaign doesn't exactly help in that regard with it being tied around a love triangle or how the Chaos campaign is centered around a pirate on the seas when the faction is largely swamp based and only has the neutral Pirate creature for the theme to go off of), or give a great conflict that all of the factions would contribute to solving, thus giving no sense of closure. There are some decent stories in the other campaigns, but otherwise it's kind of lackluster.
One thing that a lot of fans praise is how the graphics look, but I have to disagree with that. Sure, the environments look nice, but I can't say the same about the creatures. With the 3D graphics being new to the series, it's bound to happen that the creatures would look awkward, but they're not exactly pretty to look at, especially if you zoom in. Some choice examples include the
fairy dragon's feet looked webbed like a duck's feet and their wings not looking condusive to flight, the
elf having stringy hair and looking angry, the
leprechaun having a demented look on his face, and the
earth elemental looking like a combination of the Easter Island statues and a bobblehead. Overall, the creature graphics have a lifeless and plastic look to them, which I wouldn't call easy on the eyes.
There were also some odd things that the game did differently from the others: there is traditional fog of war alongside having to uncover the map; morale now helps to determine turn order in combat; the marketplace is now in the map menu (which threw me off for the longest time, making me think that there was no marketplace at all); the camera is no longer in the top-down perspective, instead having an angled look to help justify the 3D; you are never notified when a new week or month passes (which also threw me off); and turrets have be given creatures to man them in siege battles. There were a few positives: caravans can bring creatures from a map location or a different town and bring them where you want them, and it's nice to be able to flag weekly resource generators without forcing a hero to visit it every week. Those are two changes I would've liked to see in future games, though only the former got added to expansion packs for V when there were fan complaints.
The game also had a few bugs and errors during gameplay. I only encountered a few of them while playing, and it's largely a symptom of the game's rushed development.
About the only thing that fans can agree on is that the music is great, but with a few exceptions, the series soundtrack has always been like that.
There were two expansion packs during Heroes IV's short life: The Gathering Storm (2002) and The Winds of War (2003). Both added new maps to play, neutral creatures (though largely three at a time), map locations, and campaigns, but the campaigns plots had virtually no connection with the original game's campaigns, and the amount of added content feels light in comparison to other expansions in the series, and some have even pointed out that the content could have easily just been added with patches.
Heroes of Might and Magic IV is not a bad game, but it's potential was squandered due to factors beyond it's control, and its true potential may never be realized, and with 3DO's bankruptcy and Ubisoft's acquisition of the Might and Magic license, it's a sad ending for the original developers.