We did the 4 day trail and I would rate hard instead of moderate given that you need to carry your gear and there is quite a bit up & down (we saw several people need to ride the mules back).
Totally worth it but be prepared (you can find several blogs online with lots of good details). It rained 2 of the four days which was a nice break from the heat but made for some slippery trail (and you need to cross the river to the third camp prior to the rain starting.
We did the 5 days hikes and we were very happy! 4 days can be really tough! Do not take tour with the indigenous since they are not there to help you if need! One person of our group had a knee problem and had to be treated by an other tour guide. Pack light since it is very hot! Bring a liner because the hammocks are full of ticks. Do it before it get too commercial...!!!
Much more strenuous hike then the guides lead you to believe (we did the 4 day). Especially if it rains. This is one of a small number of trails out there that isn't overly crowded so get in there before it becomes so. Easy to find a guide in Santa Marta which I would recommend over trying to book online. There will be a lot of mosquitos and mud so prepare accordingly. Tip: bring a really light sleeping bag as the hammocks aren't very clean.
One of the best hikes in a lifetime, a classic combo of adventure and beauty.
Went in early February, in the dry season, and mosquitoes were way less an issue than expected.
During the rainy season this trail could definitely get rough, as much of it is steep, soft dirt that would make for tough passage.
Shoot for 4 days, easily doable!
You can check out my trip report in the AllTrails Journal at http://journal.alltrails.com/post/44281243631/hiking-to-ciudad-perdida-colombias-lost-city