I think Janet is quite...liberal? It's a practical language, but doesn't force a specific paradigm on you. There're "escape hatches" in different levels of the language, and I like that.
Maybe the most "opinionated" things in Janet are the ev stuff and fibers. I think they're done right though, you just need to be careful with the event loop when embedding Janet.
How it compares with Lua?
Strictly better unless you need an extremely small runtime rather than a very small one, or are exposing a scripting API to users who will recoil from prefix notation.
If you like Janet and Lua, might as well try Fennel, which was made by the creator of Janet.
I have read about Fennel many times and considered on trying it - I didn’t know that they have the same author!
This one actually has real arrays (mutable and immutable)