Robert K - we just got home Sunday from almost 2 weeks on AC. Best trip we ever took - you'll love it. We stayed south of town, never made it up north, just chilled most of the time. Our favorite place for supper was Casa Picasso - great drinks, tapas, pastas, and the desserts - oh my! Just not sure how romantic you would consider it - very comfortable and welcoming place to spend some time enjoying the whole experience.
We also did the snorkle trip to Hol Chan and Shark-Ray Alley with 2 different guides. I would definitely recommend Alphonse - he'll give you a shark to hug! We booked him through Monkey Business at Banana Beach.
Enjoy!