Solo Dev who responds to most reviews himself so I will give a fairly indepth rundown, may make a forum post with more specific things to point out.

Minor Spoilers in the Pros/Cons, Major spoilers will be noted below them.

CONS (get the bad out of the way first I suppose)

-The Gameplay is okay but being limited to 4 units who often overlap or are even outright better than others make it get stale fast.
-Some of the levels have really odd tuning, Medium 18/19 are super hard due to having the single most dangerous enemy combo in the game (massed muskets with a strong frontline) and absurd enemy amounts, while Hard 19 is way too easy as it relies on spamming enemies you can easily squish by that point if you have the right setup and upgrades.
-The Spelling and Grammar could use another run through but I'd be willing to point out where some spots that could be changed are.
-The resolution is strange and the game only runs in a specifically sized window (this is apparently due to the way that the game's art was done).
-The Grinding after you finish Hard 20 is... a bit much. If you want to unlock all unit dialogues expect another hour or so of grinding Hard 20 to get enough essence. Not needed to finish the game but see below as to why I note this as a con...

Pros

-The story is excellent and told in a somewhat nonlinear manner. You have the pieces of a puzzle and it's up to you to try to put them together and figure things out. Seriously, don't skip the unit dialogues or archive entries, they're the best part of the game.
-The Art is minimalist but works really well, especially with the main character and the more elaborate visuals.
-The game has a great mood to it, especially when reading the grim codex entries in the tower between levels.
-It's free, seriously, try it, it will take maybe 5 hours to fully clear at most.

Major Spoilers beyond this line.

I'm really hyped for a sequel or followup, the game leaves most of its questions unanswered and keeps you wondering about Sofia's intentions and plans, as well as the fate of the deep ones and the odd connection between the Necroshrooms and the Empire Souls. Even the question of "Is the Sofia we are controlling the whole time even the original?"

Even if it takes a while, I'd be willing to pay for a followup set in this universe.