We stayed at both the Centro Historico and Maria Isabel for our anniversary a couple months ago. We originally planned to spend the whole time at the Centro Historico, but there was a sulpheric odor that permeated the public spaces -- it was really pronounced, but no one at the hotel claimed they could smell it. We left even though we loved the room with the view over the Almeda and the excellent location (would second the Cafe Tacuba recommendation, though Cafe Popular is very funky and fun as well -- a real institution closer to the Zocalo).
We left and went to the Maria Isabel -- a huge mistake. The room was awful, the place depressing, and we were billed when we availed ourselves of the lounge (which I had been told PMs had access to -- turns out access does not mean you can actually take advantage of anything there). I would not go back to the Maria Isabel until they do a MAJOR renovation. In retrospect, we should of put up with a little sulphur
