The game is shaping up quite nicely. One bit of criticism is the (lack of) level of animation added to the bosses, adversaries, and other elements. A lot of animation is implied through overall transformation and effects, but it leaves a lot to be desired compared to the quality of your cartoon game art.
Take Dr Terrestrial, for example: it's basically a static head. When hit, it lights up, but that's it. The eyes don't move, the body doesn't respond to the action. If you'd separate all the parts, and animate them separately it would add much more polish to the final result, and make the game characters feel much less static looking.
Or take those blob enemies: merely transforming in the y-axis looks too simplistic. Their eyes and brows could be animated, and the body controlled as a mesh.
Have you considered the use of Spriter? It's a shame Construct doesn't feature its own animation timeline tools, otherwise it would be a doddle to add.
Anyway, I feel adding more animation to your world and characters would make it look much more polished.
Keep up the good work!