This is a wonderful resort with pristine beaches. We have been here 5 times in 8 years. There are always kids for my kids to play with at any time of year. The resort is very safe and laid out so you can see both pools, the beach and the game room at once. The rooms are spacious and clean (you can upgrade from a regular room to a 26/28 line suite or lanai suite for a small fee - but you get a great room!
My only gripe is the "don't ask don't tell" culture - no helpful hints or info into hotel offers are given without asking specific questions (Even with upgraded Marriott status).
A few tips - get in good with the pool wait-staff from Quinns, otherwise you will wait at least 20 minutes to get someone to take your poolside order; Buy the endless drink cup at Pazzi's; definitely take an excursion or two off the beach - but don't ride the Jet ski's - you can only go 8 buildings down the beach and it's not enough space to really get going.
Hint: You really don't need to leave the resort and parking is pricey - so rent a car at the airport from Hertz and return it at the Marriott and then rent again to get back to the airport. If you want to go anywhere on the island, it won't cost you more than $12 per ride.
Also - it is a resort - but the spa is very over-priced - $50 for a 20 minute manicure - and they are a bit disorganized there - so if you book a massage or other appointment, make sure you confirm.