In addition to all the info above... Here's the scoop on Manuel Antonio. Just so you know, my wife was born in CR and her family used to travel to MA for vacations, camping, beach, etc., The first place I ever went to in CR was MA, and we go there about every other year because of the beaches. So, we definitely have a fondness for the area.
The park... you will see lots of guides at the entrance soliciting their services, they're nice, most speak enough English, and they know where to find things in the park. I think you pay around $25 for a group of 2-5 people. You also pay $10/person (Ticos pay $2) to enter the park, and you walk along a smooth gravel path that's about 10 feet wide. Long ago this was one of the roads to the camping areas (no longer allowed). The total length of the path is about 1/2 mile and it ends at a nice little beach.
The guides will stop 4 or 5 times to point out a sloth, maybe a howler monkey or two, an iguana, a few spiders, some plants and trees, and maybe something else. They go very slow along the path. I think the tour lasts 45-60 minutes. You will see many groups, but it doesn't feel too crowded. At the end of the path you pay the guide a tip (10-20% is plenty) if you want, and they say good-bye to you. You will then walk another 50-100 meters to the beach area, and now you will likely see White Face monkeys all over the place, sometimes as close as a few feet from you. Now you know why the guides go so slowly during their tour.
The little beach is nice, many people swim there after their tour, but beware of a slight undertow if the waves are bigger than 2 feet. The monkeys in the area are entertaining, and are good at stealing food out of your daypack or off your table. No beer is allowed anywhere inside the park.
If you want, you can continue on another path that takes you around the point of land, and in this light forest you might see more WF monkeys, and some other small animals. You will pass by some nice scenery and then you end at a small river. You can pay the guy a few dollars to take you across. It's funny because most of the time the guy just walks in the water, pushing the boat across the 20 meters. Now you are at the south end of the main beach, about 200 meters from where you entered the park.
The main beach is about a mile long. It's rather busy at the south end (where the park entrance is, and the road from Quepos ends). Here you can learn to surf on the small, safe waves, enjoy the sand, get something to eat, etc. As you go northward, towards the hotels you mentioned, it gets less busy. We usually stay at Karahe, which is in the quiet part of the beach. In this area you are likely to hear Howler Monkeys. One night we saw an anteater, and another time we saw a group of Squirrel Monkeys up close. The far north end of the beach is a little rocky, and the surfing is better there. FWIW, the north end is where gay people like to hang out. If you're offended by that, just so you know. If you're like most Ticos and other people, nobody cares, and everyone is nice.
The sunsets at MA are very picturesque, partly because there is an island near the center of your photo. The restaurants are among the most expensive in CR (not counting the 4* resorts), but most of the food and service are just average. There are many options available, but none except El Gato Negro stand out for us.
There are private bus companies that take people between the major tourist areas in CR, like Arenal, Monteverde, MA, somewhere in northern Guanacaste, San Jose, etc. I think they charge $40-$70pp each segment. The buses hold 20-30 people and are reasonably comfortable and have AC.
The hotels around Papagayo are wonderful in their own way, but you will have the chance to enjoy the "real Costa Rica" after you leave there.