This is intended to be tough love not just raging, so I hope it comes across in that spirit. I've gotten more than my money's worth of fun, so it's not about dissatisfaction or anything like that, and I would support further development or Elemental2 in a heartbeat (well, as you will see, I would probably read your lessons learned posts with some interest first, but then probably still send you the moneys after that 
OK, how to begin. There are a lot of potentially awesome things about this game but, at the end of the day I just feel like it only infrequently presents interesting choices to the player. I should say, all this is just IMO and maybe others are loving it, so I will just give some examples and you can make of it what you will.
Tech Tree
Never really have the feeling "Oh I need to get XXX tech first to take advantage of my nearby environment" (this happens often enough in Civ) or "I need to get YYY to counter my rival", or even much of "If I get both AAA and BBB before my enemies it will be favorable for the long term strategy I want to do" (like in your own games including FFH2 or GC2). Yes certain bloodlines might have a couple priority techs that unlock their golems or juggernauts but I consider that the exception that proves the rule, there should be more techs that are so important, or at least more varied, and present the player with some choices with tension. End of the day I feel like 99% of the time you can pretty much always take the cheapest remaining tech and it would be fine.
Hero Level trees
Beautiful idea, but oh man are they really not coming together. So few precious XP to throw at so many passive skills. Such unsatisfying organization, like the summoning tree where the different elements are inexplicably at different powers/depths, or even the generally Blah design principle of having to take your spellbooks at the expense of actually leveling your mage. So many "must haves" like chain mail buried at random places deep on a specific branch. So many things that are 1 cool skill spread out over 3 levels. Skills that are never the right choice like +1 research, not to mention whole character paths that are never the right choice like governo. The tricky balance of power between heroes and units always feeling like it's tilting in one way or the other in combat, doesn't help I guess. But there are whole threads about this and I won't be able to do better in a general post.
Magic in general, still really not feeling it. Yeah I put enchanted hammers and magical grainfield on cities, and find whatever some killer spell is for my sovereign and use it in important battles, but I don't feel like it's caught up to AoW or even HoMM in terms of integrating in a satisfying way with the rest of what's going on in the tactical or strategic levels, again, lack of compelling decisions on a turn by turn basis. I think this is more a symptom that the city management and tactical combat game phases are both oversimplified and don't give a lot of opportunity for magic to shine, as opposed to a specific flaw in the magic system that I can point to. But the way spell learning occurs in the kinda brokeny hero level trees doesn't help. I think a system where most spell research learning takes place at the empire level and each hero only needs to have the right chanelling capability, would be a more robust system and free up hero levels/XP for fun rather than chores.
City Management
Either you need units, or you don't and you power the city. Yes there's the three types of city specialization, but that's basically a thing you do once. Back when there was building placement I thought once upon a time that there would be something really unique, like a mini "Settlers" or Zeus/Poseidon game in each city, with little agents or walkers, and local economies, but instead it ended up just going Civ style. However, it's missing the Civ style element where if you want to specialize your town, it's something that the player should keep participating in over time by either terraforming the surrounding hinterlands, or having to make choices which building occupies the prime spot, or whatever mechanic you choose to represent hard choices over time about the investment of resources and time to improve the city. Everything is abstracted away and in the end, always constructing the cheapest remaining building seems to work fine. Fortress city improvements (and the OPness of initiative) mean you are incentivized to do all unit production in whatever city you arbitrarily made the first Fortress and every other city might as well auto-govern. On level up the city trait with the long term / empire wide benefit seems always to be the "right" one.
Maybe there should be a tension between improving the local city and improving the nearby mines, but that comes to:
Strategic Resource Management / 4X
Always swimming in horses. Friendly-Unit spawning lairs tend to be actually undesirable in the medium turn. Crystal and iron almost strike the right balance but the +1 production options on level up are kinda blah. Not to mention that the two are basically interchangeable as a military resource. Systems that connect the strategic resources more to the city management game would be cool, like an alternate smelter upgrade that converts the extra production to a civilian benefit, or mid/high level buildings that have resource cost. Spend horses/mana over time to create arable land? Spend iron over time to build roads? I don't know, anything to connect the strategic resources to make the empire building game richer. Twilight apiaries are good, again, sort of the exception that proves the rule. Even the choices in the otherwise simplisting Warlock game where you have to make a binary choice about how to exploit resources (Horses resource -> improve with Cavalry stables or Merchant's guild?) are interesting by comparison.
Shards are supposed to be this key strategic resource but given the way Heroes and spell learning works, you just take whatever you find and OK it is a passive boost. The missing element w.r.t 4X paradigm is the "Exploit," I never feel like: OK here are the resources available or nearby, now what strategic choices does this inform? It's just: is there enough iron and/or crystal and at least one horse? Check, good to go.
Outposts, I guess they are supposed to take the role of improving the city hinterland, but I feel like they're kind of stuck in a local funness minima. The upgrades are slow, they're so easily conquered. It would be nice if they could meaningfully be defended by a couple archers and a local garrison (tying in to a better tactical system with say, walls and cover? Age of Wonders style chaneller's magic-projecting palintir crystal, or mercenary militia available, so that you can choose to burn mana/gold to protect it?) But as is, it's just, blah.
At the border of strategy/tactical game: No real compelling logistical / army composition problems to solve, you never need to get siege engines, heavy infantry, or elite magical special forces to the front lines, the needed phalanx or pikeman or crossbows.... because the only thing you actually want are the latest heavy cavalry and a couple horse archers. Along the same vein, unit design kind of a chore, you're just balancing the precise loadout of your best cavalry unit to match your specific crystal/iron income rate. Blahhh.
Tactical battles
Well, this has been discussed to death, they're slightly more fun to click through now then they used to be but still shallow. Not good synergy between the abilities, pacing is too fast, no terrain, no range or favorable high ground, swarm is a poor approximation of better flanking/cohesion rules, new weapon AOE strikes are sort of strange and interchangeably overpowered. A good tactical combat, besides being fun in its own right would boost other elements of the game along with it because it would tie all the strategic level things together, but I guess it has never been the priority, and I don't really hope much for it at this late stage.
Tying it together
And then, of course there's the Ace in the hole -- the unique roleplay/rpg aspects of Questing, conquering the Wildlands, and etc. But,
(1) Rewards for conquering the Wildlands are kinda blah, space for one city? Essentially the same or less impact as you get for clearing a bandit camp on turn 10.
(2) Diplomacy is simplistic and dogpiley and there's not a good way to use diplomacy to buy yourself time to quest.
(3) Tower victory is easy compared to preparing an expedition to clear a dragon or Wildland.
(4) Challenge from boss fights is generally just sort of a DPS check, well, this is connected to the blah tactical system.
Personally I feel like a more fundamentally sound foundation of first rate tactical combat and/or first rate empire building would be better in the long run, but also if "just" some combination of those loose ends and other mid/late game were fixed up, a lot of the other problems could be overlooked, and it would be in the end more than the sum of its parts.
Best of luck, much respect for you guys and your hard work, hope something in the long post was useful one way or another.
