At least when I've written elisp, the default datastructures have involved a lot of work to construct and manipulate, and when you do it right, the ones you've chosen for convenience may perform so poorly that you have to go back and change them to get your program to complete in time.
Namespaces for vars and functions being not a language feature is inconvenient. Unless you are using fakespace or intern-symbol (it seems hardly anyone does), every symbol in your program needs to include its namespace information in order to avoid it being accidentally invoked by somebody else, or accidentally convincing somebody that it's part of the base distribution.
In Clojure, it's many little things:
Keywords are callable, allowing you to evaluate a keyword on an associative collection like hash-map, or traverse, in an obvious and intuitive way, into a nested associative structure with the threading macros "->" and "->>".
The default data structures are fast (for what they are) and hard to misuse: unless you ask politely, you are not going to mutate something your function was passed passed without noticing. seq, the interface for sequences (vectors, lists, pairs from an associative structure), pairs well with destructuring in let and macros/syntax that does binding.
Things like 'let' don't use more parentheses than necessary, which has a greater impact on readability than you'd think. The use of vector syntax for bindings rather than list syntax adds a little bit of syntactic texture that makes reading programs more ergonomic.
I think Clojure may not be as unfamiliar as it seems at first to a person who's written other lisps before, but I have yet to meet somebody who prefers the experience of writing Scheme or Common Lisp to Clojure; nor anyone who prefers Elisp to Common Lisp.