We went there on honeymoon before flying to Cozumel 14 years ago. I liked it but our 4 days were enough, it’s not somewhere I think I’d spend more than that. It’s absolutely huge and some of the outlying areas we drove through were pretty rough. The city centre itself has a lot of Spanish colonial buildings, some of which are sinking as the Aztec built the city on marshes and the Spanish built using heavy stone. They built directly over the Aztec temples etc, trying to obliterate the cities origins but this is being uncovered and next to the cathedral in the main square (Zocolo) there are the remains of an Aztec temple. It felt safe walking around during the day time and in parts you felt like you were walking around in a typical Spanish city. The murals by Diego Rivera on the National Palace in the Zocolo depicting the history of Mexico were fantastic and I’d also definitely go to the National Museum of Anthropology. Some of the hotels & bars in the Zocolo have roof top bars which give you a great view over the area.
Our hotel was central but blah so wouldn’t recommend. Quite a few Western tourists seemed to be staying in the Rosa Zone, this was 14 years ago so they may or may not be a good area now but was pretty commercialised with lots of shops & wasn’t unattractive.
DH didn’t much like Mexico City but if you like modern art, history and good food there’s a good chance you will! The only thing I didn’t like was a pervasive smell of greasy corn oil from the street food vendors but that’s really minor!