Definitely the foundation of a great fangame. My nitpicks are minor: The midair controls feels like I'm on ice in Crash 2 or 3 - a bit too much inertia, most noticeable when trying to break that one cross-formation of crates with the bounce crate in the middle over the river. The bonus section felt a bit simple, but I like that missing the slide jump was recoverable instead of forcing a restart.
You've avoided BS hidden crates like in IAT, which I thank you for. I want to say the level could have been longer, but the crate count is right around average for a PS1 Crash title. Maybe you could take the giant crate pile at the very end and spread it out through another corridor before the exit? Just spitballing.
The things you've changed are things every PS1 Crash changed from its predecessor, and you've kept all the stuff that matters. The alien aesthetic implies a lot of interesting things for the story. Very much looking forward to the next release from this project!