It's good to see a well-reasoned analysis. I'll try to go through the points and share my own opinion, as I haven't really done so before. The main drawback of Heroes 4 is the overly raw and buggy version 1.0. In fact, this is what caused a large portion of the series' fans to turn away from the game. Even now, when talking to experienced Heroes 3 players, it's clear that the impression from version 1.0 still lingers. Further exploration of the game didn't change this, and a strong stereotype formed. "Sad but true." :( Next.

1. Heroes lost their individuality, not just within a race, but within the game as a whole (This might be a plus for some, but not for me).

I completely agree. Individuality was lost. Modders are still brainstorming ideas on how to bring it back. Instead, we got advanced classes – which is great, but doesn't replace individuality. On one hand, this step saved Heroes 4 from the headache that plagued all the other parts – hero grinding. But at the same time, one of the game's unique features was lost.

2. The developers failed to find a balance between units and heroes.

I agree with this too. Moreover, I would say that the developers have never found this balance in any of the Heroes games. The base versions of all the games are considered unbalanced. There's no need to look far for examples: for Heroes 3, Horn is developing the Tournament Edition, for Heroes 4, the Dalai team is working on Equilibrium, and for Heroes 5, Moz and his team are implementing the TE. And this is perfectly normal because professional players should be the ones tweaking the balance – it's logical; the developers simply can't fine-tune this balance without sufficient gaming experience. Therefore, this is just a normal phenomenon. By the way, there is no balance at all in Heroes 2. No one, ever, can do anything about the combination of a Chaos Dragon and a Barbarian. That's the balance (referring to Price of Loyalty). :)

4. Castle siege/defense is just… something else. No further comments (it's hard to be politically correct here).

Yes, the siege is different. In my opinion, it's not better or worse, just different. Therefore, I won't comment further, as it's purely subjective.

3. All these potions of immortality, resurrection spells.

The common opinion that potions of immortality trivialize the game and turn it into a battle of one super-hero has long been refuted by tons of online battles. If we talk about micromanagement in general, then this is both a minus and a plus. Resurrection spells, monsters on the map, delivering artifacts, and so on – all this greatly deepens the game, thereby increasing the difficulty. But at the same time, it increases the time spent on a turn. As a result, we get increased complexity and interesting gameplay on the map at the expense of time. To each their own, as they say.

5. Lack of the ability to upgrade creatures.

Again, this is purely subjective. I'll try to answer like this: Heroes 4 is so much more complex than the other parts (again, a fact recognized by fans of Heroes 3, so as not to start a flame war here, for example, Horn), that upgrading creatures would make the game even more complex. From my own experience, I can say that the available range of creatures is quite enough to make you think. I think I'll refrain from commenting on point 6 :D In conclusion, it can be said that yes, NWC released a raw, revolutionary version 1.0, which is bad. The game was subsequently refined, of course, both by the developers and by the players in Equilibrium, but many didn't see this, unfortunately. At the same time, the game turned out to be much more complex and deeper than the other parts, which is good on one hand, but on the other hand, it scares away newcomers and increases the game time. That's it. :)