You're walking through an amusement park. All the rides around you look wonderfully scary and thrilling; they taunt you as you pass them, they promise something different, something new, at journey's end.
The final ride is a fiberglass pony in front of the supermarket.
That's the "Los Sin Nombre" experience. You, the viewer, watch as the protagonist follows clues to find her daughter -- a girl supposedly tortured and killed but now, 5 years later, apparently living. With the help of the detective who handled the original case, she stumbles from clue to clue and into...uh...well, it gets hazy. A cult dedicated to "synthesizing the ultimate evil" through "the final atrocity" and "mastering pain", because "evil is a key". A good idea crops up hither and yon, and gets you waiting, waiting for The Big Finish.
After some disturbing imagery, a whole lot of "Oh, yeah?" clues, some confusion as to why this guy named Toni is following Mom around, the overuse of the "choppily-edited-video-is-creepy!" effect and the introduction of a character whom we're asked to care about and then gets whacked, the final reveal arrives...and then...uh...the movie ends.
But the final reveal is so totally mundane in relation to the rest of the film as to feel as let-down, a waste of energy spent in caring how it will end.
This film is all style -- all tired, overdone style. Oooh, look, everything's bleak and cold-looking! Oooh, look, choppily-edited nightmare imagery! Oooh, look, clues on a videotape! Sounds familiar, doesn't it? Yeah, I know, I said the same thing.
"The Nameless". It's in Spanish. There's some icky stuff and some fodder for your "Call of Cthulhu" game. Your call.
Bring some coins for that pony.