If you are going to Playa Grande, like everywhere in Costa Rica, remember to reserve your hotels in advance, especially during the local holiday periods (mainly December and April). Accommodation is quickly booked, the prices are higher and as Playa Grande is in a national park you can't camp.
However, the visit is worth the effort. The beach is magnificent and has the kind of sunsets you dream about. Because it is a national park the area is relatively well preserved compared to Tamarindo: the mangroves give it a certain style and provide some rare and welcome shade.
Because the beach is immense and bare its visitors are exposed to a lot of sun. So use total sun cream, take water and wear a hat!
The ocean has lots of waves but there are times when you can bathe without getting too far from shore.