Overall this was a great trip. the first day is a warm up - hot but manageable with lots of breaks. the lake at the top of the hill is gorgeous, and worth the tough trek up.
The altitude the first couple of days makes it hard to breathe, even if you don't suffer from altitude sickness. the hike up the Salkantay on day 2 is predictably hard, and the views approaching the mountain is beautiful.
The hike down is difficult because of the rocks, so make sure your shoes are broken in or you will suffer. great meals, and a great tourguide.