@hi

There are a few vimprovements that I miss when using vi(1)

• text-objects like

ci"

or

da(

are incredibly powerful, especially when combined with the dot-operator to repeat the change

• the far more powerful regular-expressions (things like positive/negative look-ahead/-behind)

• the ability to evaluate expressions in replacements like :%s/\d\+/\=submatch(1)/g lets me do some amazingly-powerful edits on a regular basis

• insert-mode completion (being able to do things like type control+p in Insert mode to search backwards for a word matching what I've started to type)

For more info, the corresponding vim help targets are
:help text-objects
:help pattern
:help sub-replace-\=
:help ins-completion

(I regularly use both vi(1) and vim depending on what the editing calls for)