Hi granada94! My ladyfriend and I spent one FULL, LONG day touring around the ruins of
Mérida . But before I get to that, I must say that the city of Mérida itself really isn't anything very special at all. The jewel of Mérida is the Roman ruins which are mainly localized in one part of the city with the exception of the ruined aqueduct which is REALLY something beautiful and awesome at the same time.
It's a shame you're going in February because all there is to see is OUTSIDE and it will certainly be quite cold. What you're likely to do is take one of the self-guided walking tours. BUT, really, if you're just stopping there for a few hours on the way to Sevilla you won't likely see half of what there is to see. We didn't even have time to go to
the museum - which I hear is fantastic - because we spent the ENTIRE day (in April) walking all over to see everything else.
You would DEFINITELY want to start at the Teatro Romano and the adjoining Anfiteatro Romano. Really impressive structures. The Teatro Roman was completely reconstructed. You'll see photos of the thing as a big pile of pilar pieces.
If you're going from Madrid to Mérida and then down to Sevilla, you may (if you can) want to make a quick stop at the beautiful town of Zafra which is below Mérida and on the way to Sevilla.
Have a nice time visiting the Roman ruins of Mérida!
Saludos, MadridMan
http://www.iespana.es/paseovirtual/Merida/merida.htm