I would suggest using extreme caution if you plan to buy any land and or house in Mexico as the laws can changes with out notice. Some people have lost their homes in the past.
Merida is a safe place. Incidents of violent crime is almost non existent. Inexpensive living and excellent health care. The temperature is warm year round. Great Food! The food is not only mexican, it includes local Mayan culture, as well as Caribbean, and European.
If you're considering retiring in Mexico then I'm sure you've already reviewed all the pros and cons of living in Mexico. Merida got five stars from each of three reviewers on epinions. com but it's best you take some time and go see for yourself.