I took my family to Los Suenos in Costa Rica during the summer. The hotel is beautiful and the staff is incredible.
Here is some basic information. When booking your stay with 800-Marriott they will tell you that there is a shuttle from the downtown San Jose Marriott to Los Suenos. What they will not tell you is that the shuttle only runs once a day (approximatley 10:00 a.m.) which means that by the time you land you will have missed the shuttle. Plan on taking a taxi from the airport. (The Marriott hotel shuttle driver wil actually help you with this). Do not stay at the downtown Marriott. I spoke to guests at Los Suenos that did stay there and they all hated it (dirty, etc.).
You do not really need a car at Los Suenos as there are taxis from the hotel to Jaco (the local city). The taxis cost about five dollars. We did rent a car to drive back to the airport. You may not want to do this. Depending on your international driving ability (Dominican Republic, Malaysia, Puerto Rico, etc.) it may be o.k. Just remember that the Pan-American highway does not have any signs but it does have one lane bridges. And if you are asking for directions, you will need to speak spanish.
The food at the hotel, while very good, can get expensive after a while. As a result you will probably want to go into town.
Souvenirs are about half of the price in town as compared to the hotel.
The hotel has excursions available such as tours of the rain forest. We took both a walking tour and a canapy tour. Both tours were fantastic however if you are just going to do one tour, do the canapy tour. You move between 13 tree platforms sliding down cables, through the top of the rain forest. (My nine year and son and ten year old daughter did it). Incredible. Something we will remember the rest of our lifes.
In regards to the hotel, the staff was excellent and all but the maids speak english. The pool is fantastic. It has routes that turn with hiding places. My kids loved it.
One other item we did was to bring clothing and shoes, etc to Costa Rica. Please remember that Costa Rica is a poor country. All of the clothing and items were donated to the local church. Items that are needed besides clothes are towels, sheets, and toothbrushes. People just do not have these things. The hotel staff will be happy to help you with this stuff and see that it gets to the right people. We filled up a couple of suitcases with this stuff, through in some trashbags. When we got to the hotel, we transferred the items to the trash bags and then we had suitcases for our purchases.
Good Luck and Have Fun!