My girlfriend and I just returned from a two week trip to Costa Rica. We stayed at Casa Horizontes for our first five days and we absolutely loved it!
We were warmly welcomed on the evening we arrived were we stayed in the 'Romantic Room'. It was quite small, but in the best way and it sits right next to a palm tree where it seems the local capuchin troupe like to eat breakfast and hang out. Be warned: some of these guys are total rascals.
The food was exceptional. As much I love casodo (a typical Costa Rican dish), it was great to have lots of variety and vegetables. We ate most evenings with a really nice couple from San Jose (see Ericka's review below) and our highlight was watching the birds and monkeys during awesome breakfast fare.
The location is perfect, if you are the type who likes off the beaten bath. The supermarkets are 10 minutes away and the beach is just down the path. We booked a tour through Yami to the National Park that was excellent, apart from the brutal boat ride, but the that was due to the awful weather. Anyway, the return ride made up for it when we saw 3 humpback whales!
Our only regret was doing this first as everything afterwards (Arenal, Cano Negro, Monteverde) paled in comparison!