Thank you for testing our game!
Teper, our artist, also did all of the level design, and even WE were impressed by his work! All compliments on level design go to him!
The game lacks two very important features for platformers: The Jump Buffer which helps the player jump after landing while keeping the momentum, and a Coyote Timer, which lets the player be able to jump a few frames after falling from a platform. The lack of these features contribute to the "weirdness" you feel with the player movement! We knew we needed to do this but we ran out of time...
The thing is, you wouldn't have to encounter situations where you felt weird about the controls if the level design had so many parts where it requires precision platforming! The level design was good but it needed to let the player run around through 100% of it, I'd say it's currently like, 80%...
The error that showed on your last screenshot might have happened because of outdated video drivers! It's not a common GameMaker crash, it's a graphics API error!
I'm glad you enjoyed the game! And i appreciate the feedback! <3