Ok i played the first 5 levels, without being aware of your walkthrough.
First level took me 4 tries, nice short and crisp introduction into the campaign with the allied keeper system and a tough but doable bonus mission (which i didnt manage to beat in time because i thought i have to claim the whole area and never did it in time, now i realize i can just run in there in possession mode to finish it).
On the 2nd level i had alot of fun at the beginning trying to figure out how to advance. Also i feel like you really put some thought into small things e.g. at one point i was thinking "man i could really use a door to trap my imps so they stop dying so often!" then i saw the unclaimed tiles surrounded by lava... or that you added some barrels to the archers trapped on islands so they can enjoy a drink while guarding this place, how nice of you. Didnt manage to beat this one though, a huge wave of level 6/7 fairies with alot of monks crushes me every time, i was probably too slow after the timer starts.
3rd level took me a couple of tries of aimlessly walking around with the possessed tentacle until i realized that he drops gold after dying. From there on this level was quite easy compaired to the others, i totally forgot about the xp bonus from resting thing, but the bile demons and orcs i got from the temple did the trick.
On the 4th level i think my game is bugged, since when i use the first relic all of greens units die, but i dont get the message i see in the script, my creatures are still capped at 3 and he keeps getting level 10 witches back. Maybe its because i didnt use the first relic right away? I let the level 10 knight walk towards my base, quickly get the destroy wall, steal level 9 warlock, kill the other 3 mages and kill the knight with chicken spell. Then i still had both charges and used the first as soon as the tunneller opens a path to green, which i maybe have to use before they spawn? Or maybe its because i claimed the tunneller spawner quite late, like after clearing the first relic room, dont remember exactly. Also my tunnellers never stop spawning and you mention in your walkthrough that they should stop at one point, so maybe the map bugged for me way before that. Oh and i also had no idea that you can de-ally other keepers, so i would have probably never been able to beat this map without the walkthrough anyways. Btw nice use of secret tunnels and caves here to get some extras.
On the 5th map i also got stuck without your walkthrough, since i wasnt aware of the trick to make your tiles unclaimed again to get the torture room. The jump and run part to get the warlock was funny! Again a tough but doable bonus mission, a long enough poison gas corridor for the level 9 giants will probably do it. The surprise 3 level 7 thieves actually gave me quite some trouble, but maybe because i only realized them when they were already at my heart, anyways an endless rain of level 1 trolls eventually beat them. Also on this map some of the heroes completely ignored everyone and walked straight to my heart, which led to all of my allies orcs following them getting trapped in my heart room and starve. Also my own units getting trapped there continously aswell was a bit annoying, but not so much.
Looking forward to the rest of the campaign, i only managed to beat 2 levels on my own so far and appreciate the difficulty, often times i pause and really have to think about on how to continue the level.