1) painless debugging with Emacs/Slime vs Rider/VS/VSCode
2) performance & consistency of it; SBCL is fast and remains that way, I can leave emacs/slime running for months and it doesn't degrade; vs/rider... they really burn a hole through my laptop and isn't even that good at most things compared, even on really old computers
3) Re-eval; you can re-eval a region, function, file, last expression etc, during running and/or debugging, which is very flexible ; something wrong, change (or write the same function next to it with a fix; very handy), re-eval and when happy , clean up and save
4) data formats... We have had, since 'forever' had 'proxy' tooling that converts any incoming and outgoing JSON to and from Lisp lists. While in code, we only work with s-expressions and it makes life so easy.
Can't have Lisp without cons. (sorry)
What do you miss in Lisp when working in C#?