If you decide to confront the guy on it make sure you have plenty of reasons why the site is poor, the site should have a google webmasters tools account you can get in and get a shed load of info from that (duplicate pages and such - always good ammo and a big seo no no)
Validation like you say, load times, browser compatibility.
Id go in with ideas on how to improve the current site, if there willing to listen to change then you've got a good base to go from.
Hope that made some kind of sense