my god it's always fun to see toy soldiers doing what we always imagined as kids. I loved the art and the whole idea
I will only agree with the other comments about difficulty being a bit overtuned, but I won't repeat that. Instead, I think my main piece of feedback would be the controls. I kind of got the grasp of the controls after a few tries, and it may make some sense since you're a tank and the view is isometric, but I feel like this would be a lot more enjoyable and probably help with difficulty tuning if you had natural controls (like up is really up), and more so if diagonals were available. And also, I couldn't tell but it felt like the damage dealt when small was reduced (if this is false, disregard the rest), which makes sense but is also a very punishing positive feedback loop (you're doing bad, you'll do worse). I think maybe giving some more advantages other than "being smaller helps avoid damage" could be an interesting endeavor.
still, the art and the concept is quite charming and I did find myself doing a few runs just to witness what my childhood imagination always wanted to see <3. You should definitely keep working on this, maybe adding like some sort of campaign with maps and obstacles and such, it could be cool.
edit: I just read some other reviews and I think you already got all of this noted down, so yeah I'm just repeating what you already know haha