I too have enjoyed a day-visit to Mérida. The area of the ruins is great but the city itself is not interesting at all. The ancient photos of the reconstruction of the ruins is fascinating, how they rebuilt the structures, etcetera. HOW DID THEY KNOW HOW TO DO IT? The museum is good too. Didn't have time to visit - or didn't know about - the Roman Circus out of town. Ruin of the aqueduct is pretty cool too.

The site, if I remember correctly, is similar to that of Granada's Alhambra in that it's an enclosed park, you pay admission and there are lots of tourists but worth the visit.

Saludos, MadridMan