Is Teotihuacan worth the day trip from Mexico City?
Yes, Teotihuacan is worth it, but the day is better when you treat logistics seriously. Go for the scale and history, not because every CDMX itinerary needs another box ticked.
Answer
Teotihuacan is one of the few Mexico City day trips that can justify taking a full day away from the capital. The scale is the point: wide avenues, massive pyramids, heat, stone and the feeling of a city older than the modern one you slept in. The weaker version is turning up late, underprepared and expecting a quick attraction. It is exposed, busy at times and not especially forgiving when the weather is harsh. If you care about archaeology and deep time, go. If your CDMX time is already tight and your interest is casual, another neighbourhood day may serve you better.