We lived in DF (you'll soon start calling It DF, or :Day-Effe instead of Mexico City) for 5 years and had a very happy time there.
You must heed all advice about not walking around with handbag, designer clobber, I phones etc. buy a brick-phone, ditch all jewellery etc.
You really need to lay it by the rules.
There is a thriving expat community, but most importantly the locals are lovely. Mexicans on the whole are polite and fun and helpful, the food is gorgeous, especially the better street food (a lot of it is safe to eat and yum), and there are amazing weekend trips to be had to Taxco, Queretaro, and Oaxaca is beautiful.
God, we loved it there.
Crazy driving, but it has its own logic, I did drive quite happily but DH never did, LOL.
Have a great great time :)