Among the best of its kind This is the film from De la Iglesia I hold in the highest regard. I don't know if it's his best, but I certainly love it the most.
Basically, the plot centers around a Spanish priest who thinks he has decoded a message from the Book of Revelation foretelling the date the Antichrist will be born: December the 25th, 1995. And so, during Christmas eve, knowing his Enemy is powerful, he embarks on a mission to prevent it... During the course of the night he most prominently meets a fat, irreverent and dirty heavy-metal fan on the one hand and the host of a TV program centered on the paranormal (who is of course a farce) on the other.
The movie first and foremost is riddled with dark humor (right from the very first scene), all the while, we will be treated to several scenes so well crafted that they will have you on the edge of the seat either gripping your nerves or scaring you to hell.
Acting (the protagonist trio is excellent), plot (the ending will leave you thinking!), pacing (some will argue it drags a little towards the ending), characters (a priest, a heavy metal fan and a charlatan teaming up!), the heavy-metal soundtrack... everything is perfect.
I think we can safely say that if you like Raimi's/Jackson's horror days, - minus the slapstick and absurdist gore - you will love this one. Or, for example, 'Shaun of the Dead' has an scene which is essentially the same to one in this superb film. Horror fans simply have to see it.