Other people have listed what's good, so I'll just list off some things I didn't like.
Using just the keyboard for the game then the mouse for restart results in unnecessary extra arm movement.
Before the first battery on a platform, a battery in the air with no platform under it would have given your player a chance to test out the jump without risk of ramming into the platform, and thus given a better idea of what timing would be needed before testing your player on timing.
The early two pits with a narrow platform between gives, by my admittedly flawed calculations measured by playing with one hand and taking screenshots, 1/6th of a second from when the second pit shows on screen to when the character needs to start jumping. Given that the jump has a slight delay between pressing the button and the character jumping, I'm not convinced that challenge is fair. And that's before the issue that the battery on the platform sometimes interferes with landing.