To start of with: I haven´t done anything like the Inka-Trail before. 4 Days of early bed times, a lot of stairs and great fun.
One of the things I found the best was an astonishing nature. You go through a highland-jungle which has especially in the rainy season with the fogs a mystic touch. The food on the trip was amazing. With 3 great meals a day (Breakfast Lunch and Dinner) plus extra tea time you´re supplied with enough energy to hit the trail. Also good guide which really looked after everyone and had a great pool of knowledge. So in the end, even if it might be a bit pricier, it was worth it. Can´t really think about anything that went wrong. Hm, not recommendable for people who don´t like exercising or sports: You´ll sweat a lot on this trail.
One thing I would think of when you want to do the trek: Arrive to Cusco a few days earlier, maybe 2 or 3, to get used to the altitude. Otherwise you might suffer from altitude sickness which really makes the trip even more exhausting and not as enjoyable as it could be. And as usual: Take as few things as you can, you always have to carry it.