We go to Mexico every year, and have always stayed in an AI resort, usually in Riviera Maya. Now that kids are older we have to have two rooms, so we saw the $149 rate,which included breakfast, and took it. We were worried about being in the gringo tourist trap we heard Cancun was, but it has worked out perfectly!! In fact, we are still here now, and I felt compelled to write this review.
The advantages for an All Inclusive Resort: bigger pools, unlimited fare, entertainment, though we have often found the food and entertainment pretty tired at even the nicest AI resorts.
The advantages for Marriott Casamagna: beaches and water blow away Riviera Maya, Marriott beds (enough said), not as many drunks, not as much trekking over massive properties, dining options, free and reliable Internet (Marriott gold members).
We were very worried about breaking our string of annual All Inclusive vacations, but not any more. We have slept like kings, had more fun enjoying the ocean, an had some amazing meals (see Harry's Steakhouse). Yes, we have constantly been breaking out cash and signing hotel receipts, but the all-in cost is going to be about the same. Plus, not once have we been in a "cattle-call" situation, the way the AI breakfasts and swim-up bars sometimes felt. We bought some booze at the airport, and have avoided buying too many $12 mixed drinks and $7 beers from the hotel. One note; bring a tumbler or big thermal cup from home. They charge $30 for one of these at the gift shop, and they can help save a bundle.
I hope this review helps!!!!