Cancun, in my mind, doesn’t really exist in Mexico. It’s sort of a Las Vegas with an ocean or an Ibiza with Americans. Unless you’re into the hardcore party scene, it’s best avoided. If you’re into the hardcore party scene – this is your town.
No matter what, you’ll probably fly into the Cancun airport. There are now buses that run directly from the Airport to Puerto Morales and Playa Del Carmen. Look for signs that say Playa del Carmen or for the Mexican bus company Rivera. Tickets should be around $7USD (cheaper if you have pesos).
You can also take a taxi shuttle to the downtown Cancun bus station. This should be avoided if possible as the shuttles will wind their way first through the Cancun hotel zone. Due to the staggering amount of traffic and drunk people, it can take upwards of an hour to reach the bus station and will cost you more than the bus. It’s not a great way to start a vacation.