Getting to the resort was an easy ride in our rented car; we drove from San Jose and stopped just before the resort to see the crocodiles under a bridge near-by; if you really want to convince yourself that those are crocodiles rather than floating logs, buy some raw meat at a merchant nearby (there are quite a few merchants right near the bridge) and toss it into the river! Be ready to see the crocodiles leap to get the food.
The resort is gorgeous. The swimming pool is meandering about as if it was a river, making it very pleasant to wonder about it in, going under waterfalls and eventually reaching the pool bar. The water is shallow (about 4 ft I'd guess), making it nice to take kids along - depending on their skills at swimming, they could swim across the width of the "river" or perhaps have floaties to help them along.
The hotel's travel agency can book tours for you, but a more affordable alternative for the same tours can be easily obtained from Piko Travel: a car or pick-up truck with the name of Piko Travel is almost always parked right on the beach, just off the Marriott property. We bought ziplining and Tortuga Island tours from them, both excellent.
The Marina is visible from the hotel and a short, pleasant walk. The Marina is not only a nice diversion, but also a different place to grab a bite or just have a stroll.
The Manuel Antonio National Park is an easy drive from the hotel. Drive all the way to (or just past) the entrance of the park and then park your car - there are plenty of places to park; don't let fake park "employees" trick you into parking on the street, way before the entrance to the park, just so they can try and talk you into a guided tour of the park. If you prefer to have a private guide, you can get one right at the entrance. We just walked around on our own and saw capucci monkeys, racoons (mainly at the beach), sloths, birds, tree frogs. The beach is very nice if you want to bring bathing suit and towel.
If you don't want to eat all meals in the restaurants, rent a small refrigerator for your room (about $10 for a few days) and shop at the nearby supermarket; it may seem pricey compared to your super market at home, but it sure beats restaurant prices for beer, wine, fruits, bread, etc. If you travel with kids, it's nice to have milk in the refrigerator and perhaps some snacks.
The beach at the hotel is not so nice for swimming - rocks hurt your feet. But the beach is nice for collecting pink shells, scouting for marine life, admiring the pelicans diving to catch fish.
If you'd like to spend a day at a beautiful beach, try Tortuga Island tour (Piko Travel charged $100 per adult, kids were free, and we climbed onto a tender right at the hotel's beach, got to the bigger boat in no time).
The hotel rooms are beautiful, comfortable, roomy, clean. The staff is very helpful. Take a walk to highest floor (I think it's 4th) and admire the view from the open staircase, overlooking the water - it's beautiful. At night, look up and sout for bats!
Although the areas outside the resort are not all very nice, the resort and marina are all very nice and very safe - a pleasure!
We had a great time!