Cool concept for the game! I did have a hard time with the controls and every time I got the character on steep terrain the boulder would fall behind me. So, I'd have to hit q, but the movements were still labored even without pushing the boulder, so it took a while to get back to where I'd reached.
The pacing for gameplay could use some work... I could see this working really well if the character moved in a rhymical manner or if you had premade push and climb animations ... The timing for each Lighting strike would be predictable sort of like a percussion, but you still wouldn't know where it hits. The bird could fly a little slower so you could have more time to react, and you can even add a health bar on it.
The art style really works for this, and it's still a very inspired take on the theme of power... I think there's a lot you have so far that could make for a pretty good game!