Its the best stretch of motorway in the country by a long way. All motorways should be tolled in my opinion then its a fair tax, and the roads are better maintained. The more miles you drive the more you pay whereas you pay a flat fee now regardless of many miles you drive (depending on type of car). Eg two people with the same car pay the same tax, but one does 5k miles a year and one does 25k miles - its not a fair tax.
I drove from Basel-Mulhouse Airport down to Marseille during the last Euros and it cost about €30 which I remember thinking was a bit steep, but the roads were fantastic, traffic wasn't a concern, and there were no road works, anywhere.
The difference between that is Basel Airport to Marseille is about 450 miles and the M6 Toll is 27 miles. So I paid about 7p per mile compared to 25p per mile at the £6.70 rate it now costs. This is the problem with PFI schemes in this country.