We were at YaYa Beach 2 days ago. They offer a couple of different packages (chair/umbrella only, chair/umbrella/drinks, or chair/umbrella/drinks/food). We got the drink package and ordered food ala carte (the ceviche was fantastic!). They offer massages, which a lot of people were doing while we were there.
They have a net that catches the sea grass so I didn't see any in the beach area. The water area is very shallow. There isn't a whole lot to do but it's a nice place with great service if you are looking to relax.
There were a lot of vendors that came by but not at all pushy.
There were 2 ships in port the day we were there and it was full. I would recommend making reservations in advance, although you don't pay until you get there. They are also open a bit later than some of the other places, which is nice if you have later port times like we did.
It was about a 10 minute cab ride and was $4/per person each way.