I confess I've been playing a lot of AOW3, so I apologize if anything here is out of date, but here's what I like about LH:
Customizing units (both equip/skills and colors/appearance)
Upgrading existing units
Playing a game and running into Sovereigns and Factions I created.
The architecture to add so much more basic content (weapon types, research, etc)
The tactical combat--I realized playing AOW3 how much I like the loss of models impacting how much damage a unit can do.
The diversity of resources (iron, horses, gold, etc.), though I wouldn't mind rare ones like mithril and adamantium (like MoM) that enhanced weapons.
Here's what I don't like:
It takes forever to get ranged units--and even longer to get ranged magic units. I know it could be a mod, but I'd like to see more progression in both magic/non-magic ranged units. Slings, short bows, compound bows, long bows, light and heavy crossbows, barbed arrows, poison arrows, etc. Or fire (or whatever) spark, bolt, beam, ball, blast, shower, etc.
The game is called Legendary Heroes, yet the emphasis seems to be on building huge armies and taking a single hero along. There's nothing legendary about that. I would have preferred a game where stacks are more likely to be groups of heroes/henchmen and maybe the occasional army unit thrown in until I can recruit another hero. This game actually penalizes you for having two heroes in the same battle....
No itemmake a la MoM. I would love to be able to quickly and easily redesign the "loot" found in the game. So much of it is oh-god-so-un-legendary. Rusty pants? Really? 4 of them in one game?
No Steam workshop support. This makes running my Torchlight mods incredibly easy. They update themselves. There are too many brilliant mods (kudos to you authors out there) that the game should be played with--henchwomen, swamp tile bonuses, bridges, summoners, etc.
The Governor path. Great idea, but having to stay outside of the city to get XP is a pain (and counterintuitive).
Not being able to blow mana on creating items for my heroes.
Not enough random events, even with the option turned all the way up. (Though most of the ones we have are fun.)
After playing AOW3, I wish there were more unique skills for units/races. In AOW3 each race's priest has a range attack of a different type (poison, fire, spirit, etc), for example.
No research or quest achievements to make things cheaper in the ol' hero store. (I have 3000 metal and make armies with enchanted weapons, and you can't give me a discount on some chain mail? Really?)
I would happily fork over $$ for the following DLC:
A GUI to select an in-game model and create a loot item out of it, and modify existing loot items.
A GUI to modify the research tree (for a single faction or faction-wide).
Off the cuff, my $.02