Game Maker. I'm really familiar with it, and I don't foresee it causing any problems for this project (those already mentioned have solutions which I just haven't implemented yet).
This looks interesting. I didn't play it much since it didn't had AI, but here is my thoughts so far:
Thanks a lot for the write-up. I'm mostly interested in UI advice right now, so this is really helpful.
UI
It works but isn't really nice to use. I didn't like how I had to choose my character by clicking and then move mouse all the way up. If the possible actions are going to stay low like they are now, perhaps you could introduce pop-up or button wheel around the selected character? It would be more intuitive and faster and easier to use IMO.
Actions are going to be capped at 8, so this is certainly doable. I'll try this out, since selecting actions is one of the most problematic parts of the UI right now. I've mostly been using the number keys to select actions, but that requires some familiarity with the system...
Another similar thing was how end turn button was placed to far right top of the screen which makes it to be far from most of the UI actions, while it is used pretty often.
Well, I don't want it to be pressed accidentally. I'll need to think about this.
Another thing which I'd like is to grid attack and move range.
Easy change, no reason not to do it.
Also, grid should be other color than the ground. Traditional blue might pop out better.
Blue ground may end up being just as common as green ground, but it's an easy change to make, so I'll try it out.
This may be just my opinion, but I'd prefer HUD to be on bottom of the screen rather than top.
That's more standard, anyways, so I'll do it.
Graphics
I don't know how final these are supposed to be. I liked them though I didn't like the overseer being just a monolith. Also, I didn't see much consistency with designs. There were pokemon-esque monkey and human with sword. Of course thigs might be explained with setting and story.
The overseer is a placeholder until I add actual commanders. I'm working on finding a more consistent style, but there are several categories of monsters which are each going to be somewhat distinct from each other. The only two monsters which are from the same category right now are the Boltrush and the Skillery, which are both elemental.