For AoW2 + Disciples 2+3 there are still demos out there at the bigger download platforms.
I've played HoMM4 (which I've heard wasn't a great title), Disciples 1+2 (+ demo of 3) and the demos for AoW 1+2.
For AoW, the things you're mentioned are right, but the building of new cities is probably minor (I say probably because I couldn#t finish the demos, was just not good enough), because setting up new settlements is difficult. The upgrading of the cities + spell research seemed to be nice though.
Also important: In combat, the neighbouring armies participate. Your party has a limited amount of units (I think 9, or so), and when you attack another party, then all the parties in the surrounding fields will participate. So it might be important from where you attack, because it might drag in more enemy or allied groups (incl. your own) into the fight.
For disciples 1+2 (3 is vastly different), you don't build new cities, and the only city you upgrade is your home city, and that mostly to unlock upgrades for your units. Spell research is limited to 5 levels * 5 spells (or 4, forgot), highest level spells are only available for a specific class of player. You can trade + buy spells though (from allies + random merchants on the map).
The "allies" part is not to be taken seriously. There are a max of 3 other players on the map, and there's no real diplomacy besides gifting stuff. Normally you're allied with one of them, fighting against the 2 others (and the fighting common enemies is what influences it most).
Your party is limited to max. 1 hero + 5 units. The units per empire are limited to 4 types of units, 1 close combat, 1 distance combat, 1 magic unit, 1 support/other.
You can upgrade some of them into different directions (determined by the buildings in your capital), but for some there's only 1 route.
e.g. humans can upgrade their close combat units into ...er....1 of 5 different units, depending on what buildings you built (choice is final; if you want to have witch hunters, you'll not get knights, but you can upgrade them further into inquisitors), but e.g. your distance unit goes archer -> huntsman -> assassin, no choice there (that varies between the factions).
Might sound boring, but through the campaigns you unlock the higher buildings (e.g. in the first 2 missions you can only built the second level, later 3rd level, etc), you get a nice progression and you can get used to the special abilities.
Units get experience and auto-upgrade (if you have the right buildings), so you should keep them.
That's different from HoMM, because if some of your 5000 skeletons die, then you'll have to re-fill them somewhere, but in Disciples you'll have to heal your 1 ice giant instead, so that he can later become a stronger frost giant. You can re-surrect units to, in case they die. That can make progress a lot faster, because you can buy healing and resurrection potions, and just travel faster into enemy lands, without having to go back and re-fill your half dozen of killed low-level units.
Battle is also different. You have 2 lines, 3 units in the front, 3 in the back (max.; you start with 4). Each unit can attack "neighbouring" units, e.g. the units in the front line can attach the other neighbouring units in the front line. In the line on the back the distance/magic/support units need to stand (else they can't attack anything). You then attack in the order of the initiative value of the units (so not per player, but per unit).
So there's no moving, but that increases the speed of the combats, making it IMHO less tedious (nothing more boring than having to move your high level party for a few rounds over a battle field to then kill the 1 low level unit within one turn).
If I remember right, then in both (AoW + disciples) the only real resource is money. In both cases you get it from occupied mines (or similar). In AoW you need to occupy the things by sending your parties there and kicking out whoever is occuping it. In Disciples your capital leads to a progression of your terrain in the surroundings (if you have more cities -> faster), and you can send out special (and weak) parties to occupy these mines. Means also if an ememy gets stronger in the surrounding of some mines, his terrain might spread there, and you'll lose the mine.
In Disciples you also have 4 (in expansion: 5) different type of mana resources (work the same as gold mines), and the different spells might different amounts of mana from the different types. I'm not sure anymore about AoW. There's mana too, but I forgot if it's different.
mmhh....that's everything I remember right now, I think.
