i agree with steve, it does look kinda old and discoloured. like most dairy, i've found chocolate can pick up "refrigerator" flavours, or the aromas of stuff that it's stored next to.
also, i'm not so sure if i'd buy mexican chocolate at all. ever since i saw a warning in our pediatrician's office, i'm very wary of buying any candy from mexico or central/south america. the article warned that things flavoured with tamarind, certain fruits, and chocolate contain unacceptable levels of lead. just what you don't need to be feeding to young'ins.