Thank you so much for playing and for such a thoughtful, detailed review. This is exactly the kind of feedback I was hoping for!
You're right about the upgraded roles: Flamethrower, Heavy Machine Gun and Sniper should feel like a real power boost, and we'll take a close look at their numbers and at the Samples upgrade effects. The same goes for level 1: getting 3 stars on Easy shouldn't take two dozen tries, so I will recheck the difficulty there.
On the call-in combos: the arrow-key input is the core idea we built the game around, so I not planning to drop it. But your point about it feeling like chaos without a direct reward is fair, and I will think about how to make it more rewarding and less punishing. Run animation will be fixed. I was really glad the sprites and the last-stand feeling of defending from all sides worked for you. Thank you for the kind words and the best wishes, it means a lot. How many levels have you completed?