We have stayed here four times. With and without kids, with groups of other families (one year we took over the whole place), and have recommended it to friends on their honeymoon. Marianne and Haim are fantastic, the staff is friendly, the place is always clean and accomidating, and surf lessons with Haim were great. The prices are the most reasonable in the area - especially for what you get. Your own kitchen, taxi and reservation assistance, maid service, laundry on site, and a pool.
We highly recommend the Oasis and wouldn't stay anywhere else in Mal Pais or Santa Teresa.