Everyone heading to the beaches will have arrived prior to Saturday so you should find it relatively congestion free and easy. You will, however, see a lot of roadside police ... just making sure everyone is safe and nothing to cause alarm. You might be "waved" to the side of the road for the officer to check your passports and car paperwork. All of this is very normal. A bit of congestion in the Parrita and Quepos area (but this is normal) so watch for people on the side of the road, walking and biking too. The road from Quepos to MA will be a bit congested, the closer you get to the park, a bit more severe. Have a safe and happy Easter holiday!