Can we increase the character limit? Currently, the user keeps typing but the software truncates the review and it appears only half finished on the web page. It would be great if the user could be told that only a certain number of characters remain, too.

It's likely you have a parameter set that it limiting what is shown.
The user can enter as much as they like, so there is no limit there.

More info - https://www.ecommercetemplates.com/phphelp/ecommplus/parameters.asp#reviewlength

quote:

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Limit the number of characters shown in the review

The default number of characters before the text is truncated is 255 on the product detail page. If you want to show more of the text there then you will need the following setting, for example

$customerratinglength=1024;

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Check your includes to see if you have that set and you can remove that or adjust it to whatever you like.