I agree it works best viewing Cube -> Cube Zero. I think you need to see the inside workings of the cube before you see it from the button pushers perspective. It also makes the big twist to a certain character all the more shocking in retrospect.
The best thing about the first film was how purposeless and ambiguous the Cube was. A secret government project whose construction and design was departmentalised and just continued to grow into this insidious machine with no real function. Much like the Alien, you have to ask who would make such a thing? In this case it is humanity's paranoid nature and greed.
This is an accident, a forgotten, perpetual public works project. You think anybody wants to ask questions? All they want is a clear conscience and a fat paycheck.
This may be hard for you to understand, but there is no conspiracy. Nobody is in charge. It, it's a headless blunder operating under the illusion of a master plan. Can you grasp that? Big Brother is not watching you.
^Sums up the film the best.
It is a frightening look into a society which doesn't ask questions. It is quite easy to see something like happening!!! Everyone has their head glue to their smartphone screens, just there for the paycheck. Easy to look the other way etc!
Hypercube is a take it or leave film, the idea of a 4 dimensional tesseract cube seemed like a cool expansion for a sequel, but it didn't work and it was written poorly, and executed even worse.
It tried to give the Cube an agenda and purpose which goes against what the other films do.
The cube is the ultimate example of ambiguity done well.