Costa Rica is well known for its biodiversity, and this itinerary is well designed to show it off given the wide range of habitat visited over the 2 weeks. Starting on the Caribbean coast, we spent our first 2 days exploring the waterways of the Tortuguero National Park. From there, we visited various rain forests and then cloud forests as we increased altitude, climbing the central mountain range that divides the country and then descending to the Pacific coast.
Be prepared for contrasting weather as go, from hot and (very) humid to much cooler at the greater elevations, and be sure to pack accordingly. It's interesting to see the flora and fauna vary with these different ecosystems as you progress through the trip.
As previous reviewers have already commented on, the range of wildlife we saw (and heard) was huge, and included birds, mammals, reptiles, and invertebrates. Highlights for me include the toucans, humming birds, quetzal, sloth, and some impressively sized crocodile.
The accommodation was very comfortable and very well presented and the various eco-lodges certainly fitted the focus of the trip, helping you to feel immersed in the forest. Most had wildlife walking trails that you are able to explore without a need for a guide. I'd highly recommend the optional (guided) night walks as an opportunity to see the tree frogs and other amphibians and snakes. I visited at the end of May, and decent waterproofs were essential - If, like me, you're taking cameras, make sure you have a waterproof bag for these too. Having said that, the weather was kind to us and although it rained frequently, it was pretty predictable and tended to be limited to the evenings so didn't impact on the excursions - but be prepared and aware that the itinerary is flexible to account for the weather if required.