Criticisms:
1. Game felt too easy after I realised u can just hold right and left click at the same time to utterly obliterate everything including the boss
2. Might just be personal preference but I really disliked the dissolve colours you used like the red and the grey, that effect could have looked way cooler with different colours and some glow I think.
3. Maybe some more juice, like camera shakes and few extra particles.
But overall, honestly its insane you did that much of a game during only 8 days so massive congratulations.
Also good job for making checkpoints as it quite hard to start with.