The Classis Peru trip is full-on, covering a lot of ground in just two weeks. The key sights are there, but also lots of unexpected minor sites which became highlights too.
The quality of guide will make or break this kind of tour because there is quite a bit of travelling and exposure to unfamiliar history. We were extremely well served in this department with Arturo, who was well organised and very knowledgeable, but also kind and funny.
The altitude effects must not be overlooked. Do expect to have a couple of days of feeling unwell, and recognise you may not be able to function with your usual energy and physical ability/stamina.