RIU has announced that they will be opening a new property beside the RIU Guanacaste, the RIU Palace Costa Rica. I usually love RIU Hotels, but I do not like the RIU Hotels in Costa Rica as they broke numerous environmental laws when building the first hotel. To support this forested area of Costa Rica, I wouldn't recommend staying at either of the RIU's. If you want to go to a RIU somewhere else, I would highly recommend Los Cabos, Cancun, Aruba, or Punta Cana.
You can check out the new hotel here:
I love RIU, but I would not recommend their Costa Rica hotels.