I'm going to start right on out and say I never played the original, a friend of mine just got me a copy of legendary heroes and I've been playing the beta.
And to start off... its a really wonderful game! It has that perfect mix of Civilizations, HoM&M and some of its own unique elements!
However, I do feel like there are a couple of things nagging me that (i'm sure) are quite similar for others. As well as some minor bugs, I don't normally critique things but since I got a beta I figured I should at least help out somehow!.
-Leveling: Hero leveling feels very... slow. When I'm playing once I get 3-4 levels it feels like I've hit a brick wall. I can go around questing, killing, even soloing things with just my sovereign and never level up. Hell, one time I had it on easy and spent over 20k mana on experience for my hero and barely leveled up. In fact it was cheaper to use random stat boosts till I got 5 health, then paragon level myself instead! This really makes the entire 'leveling tree' thing a bit miffing since things like Defenders feel like they can never get the useful perks till much later.
-Mage combat: When using mages vs soldiers, I can almost find no reason to prefer mages of them. They seem to lack the 'ability' gameplay that most ability-based characters possess. Perhaps giving mages (Non-champion) mana-less cast time abilities could bring more dynamic play to the field vs some of the current things they have.
-The one faction with the lightning damage per level passive: Going off on a question here... why does this cost so much?
-Unrest: Unrest feels almost like a pointless mechanic. As I play the game it seems very simple to cancel out, especially if I expand slowly and make my first champion into an administrator. The only time it feels like an issue is when my city is cut off from the capital and is my 4th+ city.
-Cult of a Thousand Eyes & Shrine Units on warrior factions seems very ridiculous: These units don't have an upkeep, and give warrior factions a very easy way to field armies with mana despite having stiff penalties to it (Thinking of the faction with increased cost on tactical spells.) thus allowing for a stronger economy by being able to rush production without any upkeep.
-Champions are rare, why do they require wages? Given how slow things level I oftentimes end up making them all administrators and just using my sovereign.
-Essence feels very strong, or perhaps its simply because of how I play. If I start a game and my starting base doesn't have at least two essences I feel like I just need to restart, its such a huge weakness not to have (even lategame!) that I don't know how I feel about it. Even on a fortress having 4 essence can allow you to enchant it to give all units +4 defense +4 attack when built there as well as +4 material to allow for almost instantly built armies (Arcane forge). Throw in the rain growth from a water mage administrator and you can use the sacrifical pit in the same city without penalty!
-By mixing the mages on my team, and hunting every shrine I could, I was able to field a full army of elemental with a hero that had every single maintained enchantment (from the halo that I picked as a trait), of which with him being an axe-using warrior led to him soloing even strong rated groups at times.
-Death Worship + a few weak enemies + shrine units = nigh unstoppable early game army with 2-3 shrines and a few easy battles.
-Given the difficulty at raising population, 1 mana per population on sacrifice seems 'very' weak. Perhaps 2-3 mana might be a bit more reasonable.
-Is it really necessary for fallen star to scale so well with fire shards? I got lucky one game and had 3 of them, I was just sniping armies all around the map each turn because I had 3 cities with 5 essence and mana generation from hell.
-Selling items: I tried selling things at the shop, and had around 30 wolf pelts. This is pretty cool, but has it been considered changing what you get based on where you sell? Selling spider's silk at a conclave giving mana, while giving gildar (+5) at a town, and (+3) at a fortress. Make the game have a little more variation to where you sell at!
-Scouts: Could these units be immune to monster attacks? I feel like they're worthless for scouting since they get anywhere near monsters (Pretty much anywhere), and get killed.
-What is a squad and a company?
-Given the difficulty of leveling up in the game, why does it feel like summoner characters are broken? I made one and around midgame I was running around with level 14 pets slaughtering everyone without a care in the world. (And the AI derps with skeleton horde and ignores the rest of your army).
These are just a few things I've mentioned. As I've said I'm still a bit new to this, and tinkering with a few combos and characters I'm making. Some factions seem significantly more powerful than others (The one that gets stats from shrines seems very weak given how small the boost really is even after some massive shrine control.) But... this is a beta so such things are expected! I'll be writing up a bug report here soon as I play a bit more, see what I can and can't recreate.