Do some searching around this site and you'll find plenty of commentary (and even a review by somebody).
Obviously, I like Mason a lot; I find I can create very good Perl code and mediocre HTML quickly, and that's fine because I don't care that much about HTML. Those who do care (or work in environments where people care) might prefer other solutions; HTML::Template is very popular among those who keep page development and Perl code at arm's length from one another, while the Template Toolkit is more in the middle, giving the template side plenty of power (and requiring more understanding for the page developer).
But yeah, Mason works as advertised, has been used for amazing sites, and is well supported by its developers and community. Have a go :)