As a fan of tactics games, I've wanted to make a game much like this myself. I love this concept, but I feel it could be executed in a somewhat less frustrating manner.
In its current state, the gameplay feels... painfully slow, which I think is a result of several factors-
First and foremost, the movement and rangefinding not processing diagonals is not very intuitive and also seriously slows down the game. I would recommend switching to a path-based system, one that determines the distance the character can move based on a radius from them rather than a specific number of tiles moved, allowing for travel and attacking in non-cardinal directions. Attacks would also benefit from this, since being diagonally adjacent to a foe and yet unable to hit them is very irritating and comes up far more often thanks to the clunky movement range.
Of course, this issue is exacerbated by the game being very melee-focused in nature; naturally, characters need to be next to something to swallow it, which inherently skews the game towards melee engagements, which are very clunky and cluttered thanks to the necessity of being in strict cardinal directions from targets.
In general, because the game is naturally going to focus so much on close-range engagements, I would strongly suggest the addition of movement-based abilities. For example, Schroedinger's pounce actually moving her past obstacles to a destination rather than being a simple ranged attack.
I would even suggest implementing a universal "sprint" action, akin to XCOM or Mario + Rabbids, letting the player give up a unit's attack/ability action in exchange for moving twice as much on a turn. Having such an ability cuts out a lot of down time where the player is just slowly walking units into position and hitting the wait command until they finally get close enough to engage an enemy. Coupled with being able to attack and move diagonally, I think that would go a very long way to making this game feel much more satisfying and well-paced.
I have a number of other suggestions and critiques on smaller things, like the questionable utility of certain units or the rather obscene and irritating abilities of the Dusk Lamia, but I would say that improving pathing, targeting and movement as a whole would be a massive boon to the game in the long run.