I loved every minute of this beautiful place; never felt so taken care of, and our room was amazing....especially the bath tub! The food was great, the Brazilian and Japanese restaurants rocked our worlds, and the service all round was the best I have experienced at a resort. Would come back in a flash!

I stayed at a 3 star resort in Mazatlan and aside from the bathroom being nicer in the Grand Sirenis, it was basically the same.
My parents room didn't have working A/C when we got there OR a working phone so they had to go back and forth from my room using the phone. Nothing was fixed for two days.
Service at Grand Sirenis was horrible. Keys stopped working and the concierge made us walk the 15 minute walk back to the front desk to get new ones. Maid never restocked water, drinking glasses, or coffee. There was 4 of us staying in three rooms and we took the coffee from whoever we could so we could have coffee in the morning, also had to start taking cups from the buffet area and HIDING them in our rooms so we had cups to drink from every night. We were lucky if we got fresh face cloths and towels.
Restaurant/bar down by the beach is ridiculous. All of the food is behind glass and ONE person serving it up so you wait about 15 minutes in line to get some cheese spooned onto your nachos and be prepared to wait about 30 minutes for any normal food.
During the games played during the day (water polo, volleyball) the men working there supervising the games were very agressive during game play.
Also, be prepared to either cave and go to a time share, or tell your concierge immediately that you're not interested (and about 5 times again later) because they CONSTANTLY try to sell them to you, even as you're just trying to book your supper times. My dad finally had to lose it on the concierge and tell him very sternly to STOP trying to sell us time shares.

Definitely won't be staying here again.

My husband and I have stayed in AI 5 star resorts in Mexico and Jamaica and this is not a 5 star resort. After upgrading as much as we could we would rate this a 3 - 3.5 star at best. Okay, where to start. I want this review to be fair but guests paying hard earned money for a well deserved vacation should be aware of what lies ahead. Just for the record we are usually easy going, not unrealistic and didn't travel with super-high expectations.
We arrived (2.5 hours after getting on the bus at the airport - delays with leaving, drop offs, etc). We had decided, before leaving, to treat ourselves to an upgrade to the advertised gold package. We had to fight for this however because they told us it no longer existed (it is still advertised online and in their brochure). This took over an hour to sort out at check in.
A la carte restaurants. All other 5 star resorts I have been to allow you to eat whenever you like in any restaurant. Not this one! You have to book your restaurant 24 hours in advance and can only choose 3! You book with your concierge who will be ready, willing and able to help you between 7.30am and 7.30pm. Well, be warned, book all your restaurants on arrival because otherwise they will be full or your concierge will disappear for the rest of your trip. We never saw the same one twice! The restaurants are grouped together, are not attractive, have no views at night, share one bathroom facility in the coffee shop (if it is raining you will get wet!). The food is okay for the most part but not great. We don't expect ultra fine dining but we do know how great other restaurants have been in other resorts - again this should be rated a 3.5 star at most. Best 3 are Japanese, Steakhouse and Brazilian. Don't pay for the French and avoid the Cajun!
Bars - okay during the day - pool bars etc. At night limited choice of 2 lobby bars, a disco bar (no thanks) and a bar in the theatre?? Only Corona on draft and no bottled beer at all - everywhere.
Room Service - Don't even go there! Over an hours wait each time we ordered and the food was never what it was supposed to be!
Complimentary wine and fruit bowl - really? Be prepared to fight for it!
Pools - For two of them you need to like the sound of loud music, pool games, etc. One is a lazy river (nice actually). The horseshoe shaped pool is nice too.
Beach - I liked it - lots of people didn't. More like a cove. No stretch of beach as such. Ocean was warm, bit stony and got deep quickly so no good for kids.
Rooms - Good size but our phone, tv and faucet were all broken. Phone got fixed but not the rest. Jetted tub just dribbled out but we gave up reporting anything else!
Spa - just to sum this up for other spa-lovers - do not expect attentive service!! We got forgotten not once but twice after treatments! Oh well.
Staff - super friendly, very smiley. Shame nothing actually got done about any complaints though!!
Summary - If you have been to another good quality 5 star resort please DO NOT stay here. You will be very, very disappointed.

We stayed at thiis resort as part of a wedding party. Hotel wedding planners were somewhat disorganized and not too concerned. Our room was ok accept for the large hole (supposed to be there for decoration I guess!) in the wall between the bathroom and rest of room. This makes it quite difficult to have privacy when doing "bathroom things"
We could only go to the same a la carte once during our stay as this was their rule, wished we could have gone to the Japenese twice. We were denied to sit together with other family members at one of the restaurants. We even had the exact same reservation time. We didn't know they were also booked there until arrival that evening. How hard is it to push two tables together??
Had to bus our own tables one night as the one waiter on shift was busy with all the other tables- this restaurant only had 8 tables booked at a time.
Buffets got very tiresome for breakfast and lunch. We tried to eat at pool during day or when out on excursions.
Only certain house wines were included in AI prices; had to pay extra for better wine.
Don't ever count on the shuttle to transport you anywhere on resort as they were often busy with new arrivals or transporting other people.
Got a promo price through conceirge for water circuit and massage , very lovely!
Friends got a better deal with more services included from spa staff walking along the beach!
Staff was not the friendliest even after generous tipping. Seemed to be short staffed almost....
Service on beach was one waitress. We ended up just getting our own.
Definitely NOT worth the AI fee.
Make sure to check you bill in advance, mysterious charges may appear!
Do this well in advance before leaving for airport.
Playa Del Carmen was great as was Akumal Bay! The snokeling was AWESOME!!!!!
Get up early to play the towel reservation game!!!