It looks like it's mostly improvements compared to Node. Definitely some better design decisions. But, not all backwards compatible.
A little bit like how Python3 offered mostly improvements over Python 2, but not backwards compatible. Took a while for everyone to move...
Hope Deno has an easier time overcoming inertia... I guess JS devs are used to quickly changing tooling :-)
If I had to choose between the two for a hobby project, I'd give Deno a try. Unless not using JS is also an option.