The weather is perfect. I've never been in a place where the weather is better. Mexico City is slightly cooler, and closer to an ideal temperature for me, but since most housing doesn't have heating, and cold concrete is as bad as ice, the winter can get a little too chilling, depending on which part of the city you live in, what kind of home you have, and how much sunlight it gets during the day. But Cuernavaca almost invariably has warm sunny days and cool nights. It's like late August in Ontario, all the time. Playa del Carmen, on the other hand, is about 10 degrees too hot, all the time. They call Cuernavaca the city of eternal spring, but I would call it the city of eternal late summer. I guess it doesn't have the same ring.
Cuernavaca has its downsides; there's not much of a cultural life here, but at least there are a few museums and a lot of history. Playa del Carmen has nothing. It's also very close to Mexico City (less than an hour), which has more culture than you could ask for. Being so close to Mexico City is actually one of the best things about Cuernavaca (next to the climate, I would say.) The advantage is that it's actually faster to and get around the downtown – southern part of Mexico City from Cuernavaca.
Over the next few days, I'll write more about some of the good things and not-so-good things about Cuernavaca. On the whole, I'd have to say it's been one of my favorite places to live.
For some earlier posts about Cuernavaca, read: