It does share the grounds with the Grand Mayan, Grand Bliss, and Grand Luxxe. They have also just finished some Bliss buildings (MP units with new furniture.) The MP pool is totally awesome! The GM pool is not close to the beach like the MP one is. They are building a new Grand Bliss pool that is oceanfront. If you are staying in MP, you can only use that pool.
We have stayed at this resort 3 or 4 times since it opened and always stay 2-3 weeks. We stayed at the GM portion for one week in 2007, but the MP portion all the other times. We decided to use our MP units instead of GM units at this resort since everyone used the same pool at that time. Once, we had 3 two-bedroom units for the family at Thanksgiving there and everyone enjoyed it immensely. The resort is very spread out, but has shuttles that run continuously.
You can rent a car, but we tend to walk to the road and catch the bus to Playa del Carmen. If you do have a car, you will most likely need to park in the Walmart or Mega parking lot when in Playa del Carmen and walk towards the beach. We have taken the bus to the Puerto Morales turnoff and snagged a taxi there to take us to the beach and restaurants. If you have a car, you can drive there. The resort is closer to Puerto Morales than Playa. We like Playa and you can take the ferry to Cozumel from the big terminal just off 5th Avenue for a day trip. There are lots of restaurants and shops on 5th Ave.
The Tulum tour is nice and Xhel-Ha and Xcaret are both fun. The Xcaret night show is awesome. With a car, you can drive to these locations as they are on the highway going south.
We have not been there since 2007, but it is on our "go back to" list for either 2015 or 2016. We will stay at the Grand Luxxe or Grand Bliss on the next trip.