Update of my previous wishlist by features from previous games, title by title. I don't think every of these things should be in HVI (because more =/= better) but some of them are worth to be in game and somehow I thing developrs forgot about some basic things. So let's go:
HoMM I
- Go back to more resources. Having only crystals is boring on long run. Yes, it is easier to balance but that is just a lazy way to create game.
- People (well, creatures) on town screens (of course we need town screens first

), so we have an illusion that towns are living place (or unliving in case of Necropolis). Not only monster in front of their homes but also some visitors at tavern, merchants on marketplace, guards at castle, seagulls at shipyards, rats on the street, birds (or griffins, or dragons) on the sky, etc.
- Cursed artifacts. Yes, this worthless items which you cannot loss (maybe bind on pickup for backpack?) but you can uncurse them in special adventure map building (and maybe even you get that way some nice artifact?)
- Artifacts pick up descriptions or artifacts descriptions at all. Now they are nameless junk for me (yes, they have names but no story).
- Unique city building plans and need to build certain buildings before you build and/or upgrade elite or champion monster dwellings.
- Thieves' Guild and tavern with (useful) gossips.
- Mage guilds. Mage skills could be changed to passive bonuses but spells should be learned from guilds (and maybe even research there).
- As above - Magic Shrines on adventure maps.
- Wells. Yes, this little unbalanced wells which gives you +2 creatures/week, no matter if they are peasants or dragons. Wells (or fountains) should be in towns, not necessary with their previous mechanics, because people needs to drink fresh water and no one sane build city without access to fresh water (demons are insane mind you

).
- Ultimate Artifacts. Yes, powerful artifacts which you need to dig up (and where went Obelisks?

), one per map, which take lots of time to locate (or just hear to tavern gossips

) but gives very good bonus to stats (or skills).
- King of the Hill AI skirmish option (players vs all AIs).
- Ability to set starting resources for every player and AI.
- I would say about Dumb AI difficult option but we already have plenty of this.
HoMM II
- Different path in campaigns = different maps or starting conditions (1 castle vs 3 AIs' or 3 castles vs 1 AI's - depending or your choice in game), different allies (strong hero or always join monsters or carry-on artifact) not just different solutions for one or two (the same) quests.
- Recruitable Ghosts and Genies... and I mean Ghosts and Genies from H1-2 were they were killing machines. Not needed to be these monsters by the names but by their mechanics (we have Black Knights in HV who are like Genies in H1-2).
- And of course recruitable neutral units. They can have one-time recruitment dwellings (like Genies in H1-2) if needed but any options to have them in army would be nice.
- I always liked HoMM2 terrian grounds - badlands, lava, desert - they looks so beatuful and has nice adventure objects oly for them (mana spring which double mana ponts amount, city of the dead, pyramids, centaur caverns on snow, etc.)
- Special town buildings (like Orchand to get more Halfings, Dungeon to get more gold, same as Statues, Library, etc.).
- Magic schools spell progress. You get basic spell on level 1 but mass spell on 3 or 4. So no more unbalance from H3.
- Lookout towers and Eyes of Magi. Where did these exploaration time saving buildings went?
- Haunting Mine and Elemental Guard spells. Sabotage Mine is nice but these two are better in long run.
HoMM III
- Ability to set up starting bonus (artifact, resources or gold/crystals)
- Battlegrounds which have differents bonuses: Holy Ground, Curse Ground, etc. and they looks very nice on battlefield.
- Resource silos, blacksmiths, artifacts merchants, Lighthouses, Grail buildings - you can see how many town structures HVI is lacking.
- And of course war machines.
- Dragons, dragons and more dragons... wait, after we get so many dragons in HV better not.
- Witch Huts with free skills but you can always refuse to get them (or Witch Huts with skill points)
HoMM IV
- Terrian in town screen depends of adventure map terrian, so we have different townscreens for same type of city but on different place.
- Neutral units should be align to certain faction. We have Mermaids already which are bounded with Sanctuary (her passive skills), so why not rest of them? This could create more town line-ups (for example replacing Spring Spirits with Mermaids or Water Elementals).
- Diversed adventure maps stacs - so while we see forexample Shark Guards, they could have Kappas and Pearl Maidens with them. After all, we have Core, Elite and Champion units line-up, so why not fight with all three types of Cores or Elites in one battle?
- Buildable mines. Why not build your kingdom from scratch? Just place some wood, ore, crystal sources and force players to build mine there.
- Pirates, Sea Monsters, Water Banks - more water objects to interact, not just two bonus sites, one wrecked galleon and Mermaids. Message in Bottle (sea signpost) also would be nice.
- Creatures Banks which resuplly after time so you can fight for treasures and units once again.
HoMM V
- Plague Tent, Fireball Ballista - unusual use of war machines (this also counts for catapult as WoG showed).
- Blacksmith which sells (for double or triple price) additional war machine.
- Skills but something from beta, were you can have 4 abilities for 1 skills and you can see what you need to get certain abillity (yes, it was planned and scrapped long before Skill Wheel).
- As above, another scrapped feature from beta - town fort screens where you could buy creatures.
Additional
- Arcomage game in town taverns or maybe even as additional duel mode.
EDIT:
Please note, these are only gameplay features. There are more things to correct and add if you look at: UI, Map Editor, Sim Turns, Skills, Economy, etc. - Game Mechanics in general.