Hortor's demo is a great bit of history for fans of the Mexican horde. The sound is very much in line with their symphonic sound on "Decapitacion Absoluta Al Falso Profeta", however, it has a much more confrontational nature to it. Vocals here are not quite like the high-pitched shrieks on their first full-length, being rather more direct and descending at times into death-like roars. Keyboards are kept tasteful, similar to the old 90's sound of Dimmu Borgir.
What makes these guys stand out for me is that, despite some of their gothic/symphonic trappings musically, their music is bloody aggressive and raw. It's comparable to the vocalist Azmaveth's side-project Beeroth, but not quite as schizophrenic with the keyboards.
Production on here is about the same as on "Decapitacion Absoluta Al Falso Profeta" - fairly killer for a demo, actually. Adunamy's siren-like vocals seem to be less prominent here compared to their later releases, something I actually really miss. Her voice is wonderful.
If you're a fan of Hortor, this is definitely worth the buy. If you're new to the band, you might want to check out their later releases ("Ancient Satanic Rituals are Crushed in Dust" is the most accessible).