I was reviewing a first question from a new user today in the review queue and wrote a custom comment that was evidently too long.
At the time of writing, I didn't realize that I exceeded the character limit in the comment field because there was no indication in the UI. The modal allowed me to submit my lengthy comment and closed the modal.
When I revisited the question later in the day, I discovered that my generous feedback was silently truncated. (Fortunately, I could repair my comment with my mod super-powers.)
Could we please either have an indication of characters used and the limit? An alternative feature would be for the textarea to be character limited so that we don't have a false sense of character capacity.