I did this with my wife, 13 year old daughter and 15 year old son. We had an amazing time and this was the best thing we did in Costa Rica.
First of all, the organization was excellent and they did a great job explaining everything to us on the journey to the start of the rafting trip. Secondly our guide (Fauricio) was amazing, very patient as he taught us how to work together on the raft, but also was really helpful in showing us the wildlife and also we felt very safe with him.
Third, the river was beautiful, very clean, with stunning views and abundant wildlife (Toucans, Monkeys, Cormorants). It was a great way to experience the amazing natural beauty of Costa Rica.
Finally, and most importantly, we had so much fun on the river - it was a blast!
I cannot recommend this highly enough - it was definitely the highlight of our vacation.