I've heard its good from somebody that lives out there. May be a bit too French, but that doesn't seem to bother us.
I ought to go.
Is it free?
Yes, it's great if you like historic racing; no, it's not free, you'll need to buy grandstand tickets for the race (You can buy tickets online:
http://www.circuit-des-remparts.com/reservations-108.html), the 'Tribune Wilson' on the final corner is best IMHO, you can see them coming up the tight bends of the hill then onto the start/finish straight opposite the cathedral). Take a picnic, there is a nice park behind the tribune where you can enjoy lunch. The Rally on the Saturday is free and you can catch it en-route or at the lunch stop. The route is released the Thursday before.
It's not too French (although no concession is usually made for non-French speakers), indeed, many of the competitors and Rallye participants are Brits and you can often see them trailering their Bugattis down/back (sometimes a little more bent than when they arrived!).