Antigua is the pretty upper class Guatemala. A lot of fun for a few days maybe a week but after that you start to yearn to get back into Central America proper, funny that after a few days away you want to get back to its higher standards of food and bars and you forget how annoying cobblestones are to walk on. This is a preserved city so much so that the mac donalds like everywhere else has to have a brass plaque to indicate the nature of their business - no big brash logos here.
Not only is the city gorgeous but it is surrounded by the three volcanoes Fuego (3763m),Agua (3766m) and Acatenango (3976m). You can get some really good hiking around here check out the tours in Antigua.
You should also check out a spanish school here its de riguer for many. Its great to be in and around Antigua for holy week or Semana Santa - in fact any populate area goes nuts in Central America for it. In Antigua make sure you have hostel reservations already as it gets booked out.