The original "Cube" is a fantastic B-movie rich with paranoia, meaty characterization, and fine over-the-top performances. It's creepy, cryptic, and cool. And it stands perfectly well, on its own, without a stupid sequel like "Cube Zero."
This third (!) film in the Cube series is part retread (most of the booby traps are sadly recycled), part aberration. It takes the bold step of explaining what the cube is - something that was never revealed in the first movie - but, since said explanation is bland, I'd rather it was kept a secret. There are some potentially interesting references to the society that exists outside of the cube, but they never develop beyond hints about some kind of political-religious totalitarian state. So, what little social commentary there is feels flat and unfocused.
What works? Basically nothing. The acting is purely amateur hour, the pacing is slow (how much of this movie consists of two nerds watching a screen?), and the gore effects, while revolting, fail to convince. In short, "Cube Zero" reminded me of a "Cube" fan-fic, a sloppy and sophomoric clone of a good movie that definitely did not need a sequel.