I've... actually been there. Only reason why my patch thread isn't properly maintained is due to a similar reason, as I wanted to get the patch out by a certain date for personal reasons and then I ended up spending so much time away from it that I haven't finished updating it. I'm not even actively working on it anymore even though I think I do need to get back to it. I even have an update for it prepped, though it is unfinished with campaign changes.
Common balancing error, buff every aspect of a unit and turning it from underpowered to overpowered.
The Black Knight, when it comes down to it, isn't necessarily that much more powerful on his own compared to other units. It's a massive complex mess of reasons as to why Black Knight spam is so irritating to deal with. The Black Knight comes with the Combat Pit, for example, which is insanely cheap for its purpose and accelerates the Black Knight's training speed from 20 to 100, effectively more than double a Goblin's training speed (As in not combat exp) for more than double the stats. The Black Knight also has an incredible Threat value, while other units have a pathetic Fear value. Not counting the obvious Fearless units, there's only four units that can stand against a Black Knight of equal level and not run away. Mistresses, Bile Demons, Dark Angels, and Black Knights. The latter two don't count for much.
The Bile Demon is weaker than the Black Knight in vanilla because his greatest asset is his 6000 Health, making him a tank. This is countered far too easily by one of his greatest weaknesses, his stun time. 5 seconds is higher than any other units, even the BK's 4 second stun. Additionally, he has extra vulnerability time due to his recovery animation being half a second, where as the BK gets up more instantly. Combine that with the fact that stunned units take double damage (with extra bonus stun time based on how much stun time is remaining) and the Bile Demon is effectively countered. To make things worse, he has the lowest training speed in the game, hungers often, and is dreadfully slow in movement. His raw damage may be higher than a BK's, but his recharge time is noticeably inferior.
This is what makes the BK OP and the Bile Demon sucky in vanilla. Understanding that first makes it easier to balance things. I would suggest dropping the Black Knight's Threat value and, as Hapuga suggested, raising the Combat Pit price. The Bile Demon could be turned into a better tank by reducing his stun time.
Also, I don't think Dark Angels are really that OP. They have insane offense, yeah, but their Health is only 3000 and they are not really spammable units as it costs 75k gold for a 5x5 Temple and it only gets the Player 2 of them. Trying to exploit that early game like the BKs isn't really possible without leaving said player vulnerable for a good while. It's more of a late game thing. If the Combat Pit price is increased, it makes it even harder to exploit as a Player would have more difficulty affording both things.
You should test the Bile Demon's gas a bit more just in case. It's been a while since I playtested it, but there was a reason why I removed it in my patch. I recall it was a little glitchy and didn't consistently deal damage, as in enemies didn't get damaged at all. I didn't like those kinds of inconsistencies so I removed it. Same thing with the Gas Trap, and I had to change the shot type to a Spike Trap actually, made it have AoE instead to differentiate it from the actual Spike Trap.
Strange. That certainly isn't the case in 1.3, or they'd be practically impossible to destroy in my patch.
There's three things to note here as to why it stirred up a lot of attention. The first is the nature you went about it, which I found concerning. Taking inspiration from one game and putting it into another is fine, but you have to properly adapt things to the game's mechanics and feel in order to do it properly. You didn't seem to be doing that, as you were just trying to get a literal translation/mimicking of stats. The issue here is like with the Workshop. The Workshop in DK1 had its own imbalances as you could sell it for gold, and while you don't get that in DK2, you have the issue of spamming ranged Traps and the fact that Creatures actively attack Traps so you can't just blitz through them like in DK1. Imagine a 7x7 room full of Lightning Traps. That would normally cost 105k gold to make and be impossible to maintain due to a mana drain of 875, not to mention mana to fire, but with the DK1 Workshop concept, its practically free.
I think the Fairy is also the best example to use to convey my point as well. You said you haven't played my patch, so you might not know this, but I also take a lot of inspiration from DK1. The Fairy is an example of that. The DK1 Fairy is a massive nuker of spells and damage, but is frail and easy to kill. A ranged glass cannon, basically. Her design in DK1 synergizes with the game's mechanics. The Lightning spell in that game, for example, hits up to 10 times, dealing 20 damage each. Drain hits 2 times, dealing 20 damage each. The Fairy has a very high luck stat, 40 if I recall, which is a 16% chance to critical with each of her attacks. Combine that with the multi-hitting spells and she can easily add up damage.
The question then becomes, how do implement this into DK2? Well, what you tried to do is give her the same abilities as in DK1, but it doesn't really work effectively. Lightning is a stun ability while Drain works based off of Health, which the Fairy lacks. Heal was a self-cast spell in DK1 and helped her survive a bit longer, where as it doesn't work nearly as effectively in DK2 for the same purpose. Especially as the game glitches for non-Warlocks/Monks, making it so other Creatures can't cast it on themselves. (Skeleton Army has a similar issue with non-Dark Angels) As a result of the changes in the game's mechanics, the Fairy with your modifications doesn't play out the same way as she did in DK1. She doesn't follow the same concept.
Meanwhile, the Fairy in my patch does resemble the DK1 Fairy. It was tricky to do as DK2 only allows three spells, but I managed to do it properly. I gave her Hail for good AoE control and to add to the chaos of battle. I gave her Thunder, which is an alteration of Lightning. While Lightning is ideal for stunning with its low damage and recharge time, Thunder is more focused on damage but sacrifices the stun advantage with a higher recharge time. This also makes Thunder especially effective in the water, which adds to the Fairy's damage output. Additionally, Lightning-type damage and Drain pierces Invulnerable. Lastly, I gave the Fairy Super Meteor, which is a personalized spell for her. It is powerful to suit her purposes, but also has a low recharge time to allow her to attack more frequently. The frequency of which she attacks combined with the damage she deals is important to note, as it goes with the whole nuker concept.
Do you see the difference between the two Fairies? This all changes because of the approach taken on the ideas, as it changes the final execution. The first thing that bugged people was your approach on the implementation of these ideas.
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The second thing that bugged people was that you weren't addressing everything. You ignored Creatures like the Goblin and Salamander, which basically made them dead weight units. There's not much point to trying to achieve balance with some things and not others, unless you're making small number of key changes like with the Black Knight's Threat value. You were creating a significant amount of changes, and a lot of them weren't really necessary. All they did was change the feel of the game, which is what makes them more radical.
The funny thing about DK2's balance is that you can easily counter it in a multiplayer match. Remove the Temple, Combat Pit, Graveyard, and maybe Prison and you're essentially good to go. But with all the crazy buffs you added, a lot of things became OP and the game is more or less split between super OP, OP, and UP without much of a middle ground.
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Lastly, you were tying it in with your general improvement mod. Not much to say on that that's already been said, just restating that as it was the third reason for people's criticism.
I tend to dislike sequel games if they basically repeat the mechanics of the previous games. There needs to be some changes to the mechanics else there isn't much of a difference between a sequel and an expansion. DK2 succeeds in this with changing of things like how Traps and Doors work. It fails as a sequel because of certain changes that cause it to lose the same atmosphere/feel as the original game. These are things that you cannot easily fix without radical changes, changes beyond even what I did with the editor. Meaning you can't really appeal to people that dislike DK2 because it loses atmosphere from DK1 without displeasing DK2 fans that are happy with the game as it is.
It isn't so much that the Workshop is inferior, so much as it is that there exists some OP things like the Combat Pit that make it an inferior option. In my patch, Traps and Doors are essentially about the same, even costlier in some respects, and it is still an incredibly viable option.
I'm going to say it right now. I hate vanilla DKII with a passion. I don't know if anyone can hate the game as much as I do, and that is a very bold statement to make. I think the game is massively overrated. Aside from the obvious problems the game has, what makes me despise it so much is the amount of effort that went into the game, or lack thereof. The statistics reveal all with their blatant similarity and laziness. I think the Salamander's Level 8 Fireball being weaker than a Warlock's Level 1 Fireball (225 vs 300) is my favorite example of this. You don't even have to play or work with the game as much as I have to know how little effort was put into a lot of these things, but it does help in revealing the faulty coding in many creature related aspects. I'm baffled that I could even progress my patch as far as I did with the way I feel about the game.
Yet, despite everything on how I feel, it is still important to acknowledge the differences of opinion and that some people simply like DK2 over DK1. To that end, in all fairness, yes I do think that you should release a separate version for your mod.