Validation::Class has a very helpful and responsive author. Questions are answered fast and bugs get fixed fast as well.
My rating seems a bit off, overall I give it 5/5, but the specifics are rated at 4/5. That's because there's always room for improvement. The reason I'm rating it 5/5 overall is because Validation::Class is by far the nicest validation module available.
I mainly use it for HTML Form validation and I'm aware there's HTML::FormHandler as well that actually just does that. In fact, there's nothing wrong with HTML::FormHandler and it might me easier to use for form validation. But I need to be wary of memory usage and speed and since HTML::FormHandler uses Moose, and Validation::Class not it was easy for me to make a decision.
In my quest to find a validation module that doesn't use Moose Validation::Class works best for me. I've seen modules that try to validate as soon as data is being passed to it and generate a list of errors. This is not always desirable. For example, if you're editing an existing form you want the data in it, but only validate after the form has been submitted. With Validation::Class you can just do that: prefill the data, fill in the form, and validate after form submission.
Another neat feature I use all the time are profiles.