Fantastic in Every Way

The service work done was surprisingly fun - lifting rocks and building walls with people you met two days ago is a great bonding experience! - and I really felt like I was making a difference, not just doing stuff to do stuff.
The hike up the mountain was definitely not the most enjoyable part of the trip, because I'm not terribly athletic, but the mountain guides were understanding and let us stop when necessary to catch our breath/refill water bottle/etc.
The food at all three hostels was fantastic - typically, the meals reflected the region we were in and were always delicious, without exception. They were also all very accommodating in terms of dietary issues.
The best part of the entire trip, however, was the homestay - my family had three kids (a 16-year-old, an 11-year-old, and an 8-year-old) and we all got on very well. My French definitely improved, and my mère d'acceuil taught me how to make crêpes one morning, which was really fun.