Cocolores is my favourite restaurant for supper. Yolanda,of the recently closed Taironas, is proving fresh pasta to them, so you can still get her fantastic food. Also I love thier starters bruschetta, clams in white wine. For a main course, my husband always goes for the shrimp in cocoanut, I love the grilled squid - they cook it perfectly.
For breakfast or lunch - Monte Sol soda for traditional CR food, or the place that is in the location that Buen Provecho used to be does great food, the smoked fish sandwich is what I laways have.
The new pizza place next to Chicos bar has done a great improvement on pizza.
As another option - take a trip to Cobano, Diamante (which everyone knows as Las Piscinas) is a wonderful setting with a huge patio aside 2 swimming pools and the owner used to be the chef at Sano Banano - so you get the great food at a fraction of the cost. It's worth the taxi fare - or even bus there and taxi back to save a bit
Sano Banano & Playa Artistas are good, but I find overpriced for what you get - the prices are equal to or more than you would pay in North America