Fennel really is great, and a great way to get into the clojure family. My biggest gripe with it is that debugging is the typical transpilation bed of needles. The bridge between Fennel and the Lua VM is super fragile, and it just doesn't have half the quality of the Janet debugger and REPL. It's a real shame, because Fennel is way more portable, and thanks to LuaJIT is capable of breaking SBCL's jaw, which is absolutely fucking insane. But the transpilation experience just completely kneecaps it imo. There are workarounds you can do, but even if you mess around with implementing a debug.setinfo you still run into less-than-fun edge cases like with match-blocks.

I think there's a lot of value in forking LuaJIT2 and reworking the debugging and error structures within to make it more suitable for language transparency. Doing so would make languages like Fennel much more attractive.