Almost went there for Christmas holidays. Main goal was Teotihuacan which was the Sun and moon pyramids. But Mexico city itself seemed appealing.

Traveling with family and too many safety concerns about mexico city from the lonely planet guide and tripadvisor and other online forums incl:
-Keep your camera hidden until using it.
-Do not hail a taxi. Cops known to rob and assault tourists.
-Do not go in a underground walkway where it might be less crowded.

Hence dropped it for now