I wasn't even going to post the leprechaun, I wanted a screenshot of the battle screen but google provided me with the picture and I couldn't resist
That leprechaun is "all that went wrong with Heroes IV" in one single creature. People saw it and didn't want to even think about using it because of the way it looks. And it looks terrible and is off flavor to an absurd degree. At the same time, it gives maximum damage resistance which makes things very hard to kill. Along the way people also miss that luck is damage resistance because they avoid the most common supplier of it like a plague. Then people complain that their stuff dies too easily :D Complete mess, but when you get down it, it's graphics that start the chain.
You know, I probably am overstating it somewhat. Still, I haven't played HoMM4 since whatever year it came out and it's one of the things I remember the best about it: low level heroes dying randomly. Oops the wolves can pass between these shrubs here, dead. Oops a medusa hit you, dead. Oops someone cast a spell on you, dead. Maybe it was manageable but very annoying.
This really depends on troop placement and picking your fights. Also it happened, but wasn't that big a deal if it happened. Also, I said abouve - stuff is much stronger than people expect, wolves aren't pushovers.
Some may ask - but wth they're tier 1!? Yes, in Heroes IV, but in heroes IV they basically mostly cut the fully-disposable H3 tier one unit and made tier 2 and tier 3 into "tier 1". Every castle has (at least) 8 creatures, it's just that they're packed in closer to each other.
It's not impossible to kill them but they resurrect for basically free (and the potion resurrects a level 2 and level 20 hero for the same cost) and can take a huge portion of enemy army with them each time.
Not necessarily and it also depends on how long of a scenario we're talking about. And, if they're drinking immortality they're not doing much. And also, there are spells which remove buffs from stuff, including the immortality. It's possible you cheezed it in the campaigns where you reeeeealy get to develop heroes beyond what you can expect otherwise. It's not that ressurection can't be cheezed, or that some heroes don't make rather good tanks (or that with good play you can't solo certain things with heroes), I absolutely agree but it really wasn't that big of a deal in multiplayer. Especially once you learned ways around it and there were plenty.
EDIT: Where they dropped the ball, IMO, was the "Combat" skill tree. I think they should have made all heroes more capable of holding their own without the Cobat skill, and used some of the filler slots in other skills to improve durability (if not offesnive power). IDK, but that could have been done better, lots of things could have.
I mentioned Inferno and Necro merging specifically because it struck me as a super lazy move of just making TEH BAD GUYS TOWN when it didn't really fit together. I never played the original King's Bounty, I started with HoMM1 (I think? I didn't play it much, maybe I started with 2 and then played 1, I'm not really sure), I played 2&3 the most. I don't mind units moving around but IMO inferno+necro is like making a good guys town with knights and elves together.
Then you'd be surprised that in the game which started it all, kings bounty, the "dungeon" dwelling/castle/faction consisted of skeleton - zombie - ghost - vampire - deamon (mechanically exactly the same as the genie from HOMM1/2, and with wings). It's older than you think :D Check it out, I haven't been able to find a better list (probably there is one on the net), search "PRIVATE GUARD" (player faction) and all the other ones are listed below
http://www.genesisproject-online.com/Genesis/I-k/king/king.html Heroes IV took a bunch of things back to the source material, shame it got such a backlash.
Also, the distribution in Heroes IV is very, VERY obviously inspired by Magic the Gathering in every possible way. Undead and deamons are in black in MtG, Inferno - Necro remrege is completely on flavor there. But really, Inferno was the blandest of the bland spammy Heroes 3 factions, the Efreet found a home at Chaos which was fine but you really had nowhere to go with the other guys. You had hardly anything to DO with the other guys, they're all the same bland thing, and there's noone to pair the undead up with and there's not enough undead to fill up a full 9 slot castle. I mean, the poison spitting slug deamon is Lich in disguize, but Lich is "skelleton with a crown" as opposed to "skelleton".
I'm more annoyed with the Mechanical Dragon, Faerie Dragon and Black Dragon. I wish they made a Heroes game with just one, exactly one single dragon. I recently replayed some HotA Heroes 3 maps and it's like Heroes of Might and Dragons. (There was a good reason to inroduce three colors of dragons in Heroes 2 because they really needed to make the Warlock pay for the imbalanced s**t, but it got waaaaaay out of hand and waaaaay into lazy dragon spam territory by the time of H3 expansions). Technically porting the Bone Dragon into Heroes 2 to top the necromancer off started the lazy dragon spam.