These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Broken Base: Heroes IV: an interesting unorthodox take or a Dork Age best forgotten? Heroes V: a breath of fresh air or a buggy and unoriginal remake of III in 3D? Heroes VI: Is it going to be the best or worst installment ever? Ashan: a valiant effort to clean up the Continuity Snarl of the NWC era, or a bland and generic fantasy world? Practically every mention of Ubisoft or Nival is bound to have split opinions among the fanbase. Even the overall well-liked third game gets this occasionally for its Art Shift from the more fairy-talish visuals of the first two games to a Real Is Brown palette.
With the release of Heroes VI, the broken base has been shifted to "Is it irredeemable, or can it become a good game with sufficient patching and feature-adding via expansions?".
There's a large sect of fans who despise anything that's even slightly different from Heroes II and Heroes III.
The Shadow Council voting system for the in-progress Heroes VII opens up new ways to break the base... or at least give them a defined voting percentage.
Complete Monster: Kalibarr of Heroes IV was extremely evil and tried to kill all living creatures. He used his apprentice to help him gain more power (and to kill him), but he was stopped by him in the end, freeing children he attempted to sacrifice.
When it comes to the Heroes 4, Harke is probably a better example. The guy attempts to assasinate Elwin, and when he fails, brands him a traitor, then forces his lover, Shaera, to marry him, and brainwashes the girl. It's been heavily implied that he even rapes her at one point. When he's exposed, he splits the entire nation and causes a civil war, and in the end, even takes advantage of Elwin's Cruel Mercy. While in prison, he spreads false news of Elwin's death, hoping it will drive Shaera to suicide. He did all that just because he hates Elwin.
Crowning Moment of Funny: Sir Christian's campaign in Armageddon's Blade. The tale of a perfume salesman with some military training trying to get home after being shipwrecked on an island chain populated entirely by nutcases.
One of the things the Heroes games are known for is their excellent soundtrack.
Heroes 4 in particular deserves a mention here. With perhaps one or two exceptions, the entire soundtrack is just amazing.
Demonic Spiders: Phoenixes in V. Fast, powerful, and a permanent fire shield that damages any unit that attacks it. Even worse, when the stack is destroyed, it resurrects on the spot (because, you know, phoenix).
The spell version can be even worse, though without the resurrect part.
Ghosts in II. Every time a stack of ghosts kills a creature, it adds a ghost to the stack. These are especially difficult early in the game, as a half dozen ghosts can hit a bunch of peasants, kill 20, and suddenly you're up against triple the number of ghosts you started with. Because of II's "flying enemies have no movement restriction" mechanic, it was impossible to protect yourself from ghosts. You just had to wait until you had a high level army that could take the ghosts with no casualties.
Vampires. Reasonable stats everywhere, can fly around you, upgrades can prevent you from retaliating, and ressurect based on dealt damage if they're fighting living creatures. If it weren't for the fact that half the Necropolis' army is fodder in any game, they'd be much worse to stop.
The dragons of the first game are much stronger than any of the other unique creatures of the other factions. Any wizard who can muster enough treasure to support them and secure access to a sulfur mine can storm his way through any other factions armies without too much difficulty. The dragons' dominance continued in Heroes II, though the titans did provide some resistance, though some speculate that it's not enough. Lampshaded in one of the random rumors you can hear at the tavern: "A Black Dragon will take out a Titan any day of the week." The third game's Armageddon's Blade expansion introduces four neutral dragon units. Each is in a tier of their own and they are obscenely powerful. How powerful? The strongest one, the azure dragon, costs 30000 gold and 20 mercury to recruit from its dwelling. And that's a bargain. Its special ability is to scare its enemies shitless, preventing them from taking any action for a turn, has by FAR the highest stats in the game, except speed which is still among the highest. Usually falls under Awesome but Impractical due to the staggering cost, however.
IV continues the trend, especially with the expansion-exclusive Megadragon. These guys have monstrous amounts of health (more than twice as much as their closest competitor, the Black Dragon), as well as disgusting amounts of damage capabilities and the standard dragon breath attack, which can hit two stacks of troops at once. This is only somewhat mitigated by the fact that they can't fly, they only have 50% magic immunity instead of the Black Dragons' 100% (though this means that their stats can be buffed even further by spells), and the fact that they usually can't be recruited on maps by any hero.
The Necropolis' vampire in every game. The upgraded versions in the third and fifth game as well as the vampire in the fourth game combine decent stats for their tier, the ability to fly/teleport on the battlefield, no enemy retaliation, and the ability to heal and revive their numbers when attacking living units. Although, the vampire's power might be just due to the rather bizarre way to balance the Necropolis, where outstandingly strong creatures are "balanced out" with laughably weak ones.
Arcane archers in V. They are third tier, and so can be acquired easily and early, and have the highest damage of any ranged unit when accounting for their weekly growth. Oh, and they deal full damage even at long range, and take into account only half of the victim's defence. They die quickly, but can do horrendous amounts of damage to much higher tier units before this happens.
An extremely gamebreaking combination of Untamed Cyclops and Chieftains from the Orc faction in Tribes of the East can allow you to trample through gigantic armies with no casualties. Behold◊ the results◊.
Genies in the 1st and 2nd game. Any attack from a stack of genies (even a stack of one) has a chance of halving the target enemy stack's numbers. Mitigated by the fact that genies are exceptionally rare, and don't repopulate every week.
Death knights take a similar role in V. Usually chances are calculated by comparing the total hitpoints of the involved stacks, but death knights always have a 25% chance. They are even harder to get than genies, though.
The Puppetmaster, Blind, and Frenzy spells in V (yes, V has quite a few gamebreakers). Careful use of these three spells will cripple even the strongest armies.
Blind and Berserk pretty much ruined the opposition's day in III and IV as well.
V's dark magic in general is pretty damn powerful. Even the 1st level spell Slow, which reduces the rate enemy units' turns come up, remains effective up to the late-game. Combine the mass version (which targets all enemy units) with the above three spells and your enemies are sitting ducks. All you need to do is stack mass Haste on top of that to complete the Humiliation Conga.
Also, the Order magic from IV. The aforementioned Blind and Berserk? Level 4 Order spells, but dwarfed by the level 5 Hypnotize, the granddaddy of mind control spells. One should also beware of Forgetfulness, which neutralizes ranged units, Teleport, which is Exactly What It Says on the Tin, and Steal All Enchantments, which removes all status buffs from the enemy and gives them to your own army. Combined with the ranged and spellcasting Order creatures, winning endgame battles without moving a single unit is not only possible, but usual.
How about Town Portal in II and III? It allows you to instantly teleport to any town you own, so not only you can pick the most powerful creatures from each town, but also get the bonuses all grant (increased stats, extra mana, movement, etc, etc). On top of that, it makes the surroundings of all your towns incredibly dangerous places even if there is no one around. Combine with Dimension Door, and there you go, instant doom for anything foolish enough to pop up in the map.
Earth Magic itself is a Game Breaker at Expert level in III however, with spells like mass Slow which completely crippled armies, Expert-level Implosion which is the ultimate damage-dealing spell and perma-Resurrection/Animate Dead which, especially when combined with Blind, pretty much meant a good spellcaster would never lose troops in most battles as long as he had mana. Add Town Portal to the mix and one has almost no reason not to take it because it's just that powerful.
V also has a spell that lets you teleport your army a short distance on the world map. It allows you to bypass any obstacles, including campaign-specific gates that are supposed to shield "invulnerable" enemy cities from your wrath. In the campaigns, this spell can't be learned in mage guilds for precisely this reason. It also takes up half your day's movement, so it can only be cast twice in one turn. Contrast this with III, where it took the equivalent of moving one tile.
Ultimate skills in V. Sure, they require a very specific skill development and levels out of reach in smaller games... but once you have them, you pretty much won the game, at least most of them. How about guaranteed luck on each and every action (and 25% more damage, too)?
Training (which allows you to upgrade lower tiered units into higher ones - turning a peasant into an archer into a footman into a priest into a cavalier) for the Haven faction in V, before it was put back to slightly less game breaking levels in the expansions. On paper it doesn't look all that broken, as it costs triple of what the unit normally would - until you realise it's possible to get enough artifacts to reduce the upgrade cost to nothing, giving you the ability to turn all of your peasants into cavaliers for free.
The Combat skill tree in IV. Particularly the main skill, increasing the Hero's physical defense that it would need at least a dozen top-tier units to challange him/her alone. Add to that the Magic Resistance secondary skill, that grants full immunity against hostile spells and spell-like effects at its highest level. Did I mention there is only one negative status effect (stun) that is not considered magical in nature?
Loynis one of the closest in III. Starts with pumped up Prayer spell - decently strong buff of 4th level increasing attack, defense and speed. So basically its a three spells in one. With water magic expert it buffs whole your army instead of single unit by 4 stats and usually that also means you have mass dispel in your spellbook too. Funny part is Loynis increase effect of prayer by 1 per his every level, effectively making it 5 times stronger by level 20. Unsurprisingly it makes your army wipe floors with everything comes in their way. The only risk is if Prayer is overwritten by other spells.
Sir Mullich, another Castle hero, gives everything he controls a +2 movement bonus. What elevates this to gamebreaker is that the Castle has three units - royal griffins, champions, and angels - who, with Sir Mullich's movement bonus can cross the entire map in one shot. Oh, those champions? Unlike most fast units they are not low on defense, and they get a bonus damage for each square they move.
Deleb, one of the random Inferno heroes in V. Her special ability is ridiculously powerful in the early-game and remains useful in the mid and late-game. It got nerfed, but as everyone else she also got more perks for the ballista.
Dark elves in V can empower spells, increasing damage by expending more mana. Sinitar has the catalyst ability, reducing the magic he spends when empowering a spell. With the right combination of gear and spells, (arcane training, erratic mana and ring of Sar-issus to lower mana costs, Runeforce items, warlock's luck and Rage of the Elements for extra damage), Sinitar can inflict a lot of damage on his opponents with very little cost.
The Stronghold faction in V has a particularly deadly late-game strategy. One stack of untamed cyclopses + 6 stacks of orc chieftains increasing their initiative (thereby giving them more turns in battle) = Curb-Stomp Battle.
The 'power of dragons' artifact set in V, if completed, provides heroes with a free tier 7 creature every day of the week (most tier 7 creatures are recruitable at a rate of two per week, except for bone dragons and towns with Grail structures), as well as giving tier 7 creatures a significant power boost (plus minor boosts for all other units in your army) and multiple bonuses to a hero's attributes.
Dark Messiah was infamous for how kicking enemies into convenient traps/pitfalls became way more effective than anything else.
The Conflux faction in III is really overpowered. So much so that it is banned from official tournaments! In fairness to the Conflux, it was assembled quickly to replace the Forge when fans demanded that it be changed. If it had a bit more time, then maybe it wouldn't have been so game breaking. Also, it spawns four tier 7 monsters per week, and while Firebirds are pretty wimpy (possibly why the spawn rate is so high), Phoenixes are really pretty badass. It also managed to oust Tower as a Magic Town due to Conflux's inbuilt University; while tower had a chance to give more rare spells to your heroes, Conflux could allow your heroes to master all four schools of magic for only 4000 gold!
All those examples pale in comparison with the "Cloak of the Undead King" artifact in Shadow of Death. Yes, it needs several artifacts assembled to begin with, but allows a hero with the Necromancy skill to raise, instead of Skeletons, Walking Deads, Wights or even Liches, a level 5 shooter.
Heroes V seems to have a cult following in China, with a separate MMORPG based on it released, including a Chinese-esque faction.
Goddamned Bats: Ghosts in V are incredibly annoying. They're not that tough, but they have a 50% chance of avoiding any non-magical damage. A pretty big issue early on, when your heroes probably don't have any potent attack spells.
Most factions have some sort of Goddamned Bats too, if not as bad as the ghost. For instance, pixies and cerberi, which move fast, act often and strike multiple targets that can't strike back. Or the assassin, which can decimate any valuable stack with their poison. Magic users dread the magnetic golem, which is not only immune to pretty much anything, but they even heal from damage spells and protect allies from area spells. Their annoyance factor declines in larger battles but they are dreaded as neutral monsters you want to deal with without taking too many losses.
Good Bad Bugs: The Sacrifice spell in III is reasonably rare and does not look too hot on paper (kill your own unit to heal damage to another). Fine. However, there is a bug that means that you can kill any unit to heal your own, including enemy units.
Another one in III was that a hero with the Tactics skill (that lets you arrange your units before battle) and a stack of cyclopses coud get a free shot at an enemy town's towers or walls in the Tactics phase.
Growing the Beard: While the fifth game and its first expansion suffered from lackluster storytelling, Tribes of the East featured better writing, a new level of strategy thanks to alternate upgrades, another new town, and several other tweaks to the gameplay. It also didn't hurt that Tribes of the East was a stand-alone product.
Joke Character: The Walking Dead in III. Slow, weak, and hardly used, it was more effective to turn them into skeletons instead.
Magnificent Bastard: Sandro in The Shadow of Death. He manages to trick heroes into giving him powerful artifacts, kill all of his competitors, creates a comfortable position for himself as The Man Behind the Man to his puppet king Finneas Vilmar, and nearly conquers the world. Even when his first attempt at world conquest is thwarted, he still singlehandedly lays the foundations of the Restoration Wars. Near the end, his title is stolen from him by his "puppet" king. Vilmar tricks Sandro into attacking an innocent Deyjan lord, giving Vilmar an excuse to imprison him and then take all of the credit for Sandro's plans to conquer Erathia.
Vilmar, however, botchers it when he proves to be too incompetent to rule the necromancers without Sandro to tell him what to do. Sandro, on the other hand, shows to be quite a Karma Houdini, like the best Magnificent Bastards out there, paying for his crimes with just a bit of jail time. However, he seems to get a bit of a change of heart. He keeps being evil, but in Might and Magic VIII he seems to become the leader of the Necromancers Guild of Jadame and proves to be an effective protector of the necromancer's right to study dark magic. His motives once in the world of Axeoth are unknown, but his hero description points that it probably orbits around recovering the power he had on Colony.
To be fair to Vilmar, the necromancer campaign in the third game gives no indication that he was a lousy king. True, he wasn't capable matching Catherine Ironfist's tactical prowess, but since she's established as a brilliant commander there's no shame in that. He only makes one really stupid mistake: reviving King Gryphonheart as a powerful lich in the hopes that this lich could defeat Catherine. The Gryphonheart lich immediately kills Vilmar and seizes power for himself.
Sadly (if you happen to be one of his fans), if the Sandro mentioned in the fifth game is the same Sandro from previous games, then he was Killed Off for Real in the game's backstory. His apprentice Markal, though he does a good job manipulating Isabel in his bid to take over the Griffin Empire, is too much of a Complete Monster to be a Magnificent Bastard.
Sandrogets called so by his first apprentice Lucretia at the end of "Danse Macabre" after he admits to manipulating her for his own purposes.
Narm Charm: Heroes of Might and Magic 1 had some pretty silly looking creatures, but some of the sound effects, such as the druids and turret sounding like TIE Fighters, and the peasants' monotone "Ah!" when they get hit just take the cake.
Nightmare Fuel: In the first three games, if you lost a map, you'd be treated to a scene of your own execution, either by the guillotine (I and III) or the sight of your abandoned skeleton in a cage that was hanging off a tree (II), complete with music to further emphasize your failure.
Also in the same tune is Heroes II's battle defeat scene. I shows the defeated Hero walking away from the battlefield in a rather gloomy tune. II shows the Hero running from the scene like a coward while vultures immediately pick on the flesh of his freshly-killed army. The music doesn't help either. The one from III is similar to the one in I, but a lone soldier runs towards the hero with a flaming arrow in his back then promptly falls dead.
That One Boss: Orlando, the Demon Lord you fight at the end of the Necromancer campaign in Tribes of the East. Due to a ridiculous combination of skills and the Lion artifact set, he has Luck and Morale parameters at +9, meaning that every unit will either crit or get an extra turn 90% of the item. Even with the ultimate Necromancer skill and the various artifacts you have by now, you can at most reduce this to +3 or +4. On top of that he has a stupidly powerful ballista that does about 500 damage per shot, shoots 4 times a turn and can crit. Luckily you have a massive amount of towns to draw forces from, but Orlando also gains troops with time.
That One Level: Steadwick's Fall in III. The goal is to conquer Steadwick within 3 months. The catch? It's guarded by Lord Kendal, a very powerful Campaign-exclusive hero. Not helped by the fact that the city's barricaded by heavy garrisons and extra cities surrounding the entire map.
Squick: Thralsai, leader of the dark elf Soul Scar clan in Hammers of Fate has a line that wouldn't sound strange coming from one of the dark eldar:
Thralsai: I feel the urge to celebrate. Fetch me a slave, a fresh one. And towels for the blood.
Strangled by the Red String: Raelag and Isabel in Hammers of Fate. Especially egregious considering that Raelag murdered Isabel's husband Nicolai in the main game. The awkwardness of this pairing probably contributed to Raelag being written out of the story in Tribes of the East.
They Changed It, Now It Sucks: Part of the reason the fourth game wasn't so well received was because it completely retooled everything in the series. Combat, unit production, and hero development were all changed. Oh, and it blew up the previous games' setting. The fifth game saw a return to the third's style of gameplay — and was promptly criticized for removing the few changes that were well received in the fourth, such as caravans (these returned in the expansions).
The AI was absolutely atrocious. Often it would not have even fully explored its home area by the endgame, and you would often find the mass graves of dead heroes who kept futilely attacking the same powerful neutral stack. The worst? There is chance that you will find the hero you need to kill already dead. This is reason why people at Gamefaqs add instant win cheats in the walkthrough — you might need it.
Speaking of the AI, check here if you want a laugh.
Some of the criticism of the sixth game is in this vein (for instance, criticising the reduction of the number of resources).