We stayed at the Costa Rica Tree House Lodge (the tree house building) for two nights in May 2012. This is like a child's fantasy of a hotel room, with trees sprouting up from the floor, a toilet inside a tree trunk, and suspension bridges connecting the master bedroom to the main living area. The unit has a full kitchen, two full baths and two bedrooms. We could have spent a happy week here doing the adventure tours (hiking, snorkeling, horseback riding, rafting, etc.) and hanging out in Puerto Viejo and on the beach.
The free welcome breakfast we received on the first morning was an enormous pile of fresh fruit, meat, cheese, bread and juice. Very nice.
The grounds are also stunning. On the one-minute walk to the beach alone we saw colorful crabs and many lizards and birds. Some guests have reported seeing sloths, but we weren't so lucky. We did hear plenty of howler monkeys, though.
When my friend and I checked in to the lodge, we were both sick with a 24-hour flu, and the staff were incredibly helpful, offering to carry our bags, bring us anything we needed to eat or drink, etc. We really appreciated their attention and concern.
My only word of caution: Be prepared for a rustic version of luxury. The common areas are open-air, so there's no air conditioning or protection against bugs (except in the bedrooms). You will need to wear bug spray, and you will need to keep your food covered. Also, the lodge doesn't have the services of a usual hotel, so you will need to bring your own groceries or schedule time to purchase them in Puerto Viejo. And, the bedrooms are screened but not soundproof, so you'll need ear plugs if the bugs and howler monkeys might keep you awake.