The big annoyance on the elisp front is it makes math slightly more annoying (~80% of my usage of the register).
Trying to evaluate x + y and have vim insert the result is now (+ x y), which is more key-presses. It's a trivial, but slightly annoying in my common case.
Also throwing a bunch of things into an array and indexing into the result, then incrementing a number is more complicated as well (I usually run this in a macro to process a list of things), which is another ~15% of my usage.
There are a lot of things to complain about in vimscript, but infix operators and c-style array indexing has never been at the top of that list.
That being said, in the general case, elisp offers a really nice way to integrate with the editor. Far superior to classic vim-script. It just makes the = register slightly more annoying.
But, asking someone someone to maintain an entire language interpreter just to make the = register more familiar is kinda too much to expect of someone. At least the = register is there, I've never found another vim emulator that even has it.
One trick that makes life easier for lisp is to use something like Karabiner Elements or xcape to turn taps on the shift keys into parentheses. Also, setting up nice keybindings to insert and manipulate parens. Between these two things, I’ve never found lisp any harder to enter than infix languages.
Yeah, it's not the worst thing ever, it's just weird manipulating text in command mode. The standard emacs keybindings do work, but it's not what I've spent the better part of a decade burning into my muscle memory.
Oh well, c'est la vie. Evil + slime/sly is still a better lisp experience than anything else I've tried.
They even get the = register. Evaluates elisp instead of vim script, but what are you gonna do?