you don't have to write programs in a functional style. write them in whatever way they are most natural. though i agree with/let are kind of ookie at first
in my case what happens in languages is i hit a ceiling. in some languages i hit it right away, in others it takes a week or two. the worst ceiling imo is lack of first-class functions. beside that, code-as-data is another major lisp benefit. just consider lisp a language with ceilings substantially higher than most other languages
most of all i recommend having a significant project to write regardless of what language you're learning
