From what I've played so far, I really really like this game. Broswer Unity's got issues on my computer so I played the Steam demo, which I'm assuming is the same.
The concept of coombining Mario 64 and Doom is a really out there idea that manages to work surprisingly well. There's quite a bit of depth to the gameplay and it all comes together quite nicely. The map design can be cool and even trippy at times.
The only things I'd really criticize so far, are that it's way too easy to tank a bunch of hearts worth of damage at once from enemies, especially when trying to whip skeletons.
And that the pixel art is very inconsistent and amateurish. Although, while the varying resolutions of sprites can look kind of off-putting, the way everything tweens around in 3D space is really appealing and cartoony. The way sprites layer like in the intro cutscene is also very fun.
All in all what I played of the demo was promising, and I'll probably be playing more!