I've been to the Alpi bike, photos here: http://www.flickr.com/photos/dcsolomons/collections/72157621720185821/
Mont Genevre was really good, very well thought out dh style singletracks with jumps and drops. Real eye opener to how a bike park should be built in the alps, we managed to ride pretty much everything twice in a day, wouldn't stay there more than two days.
Sestriere was freshly cut dh and could do with some bedding in. The lift is short and they only used half the lift altitude. However the tracks were great and worth a days ride.
Sauze D'Oulx was average but definitely worth a days ride. Trails were good but not maintained well and have abit too much traffic.
Bardonacchia was utter shite! We did two runs and went elsewhere. Avoid.
All in all the resorts are much better than just going to the same old Morzine. I highly recommend going by car and having a roadtrip.