Of course what's interesting re Dredd is the turn the comics have taken. Whilst the Judges are still effectively a fascist dictatorship, Dredd has definitely mellowed, and often the Judges are portrayed as a necessary evil, and those who want democracy fall into three categories; the well-meaning honest ones, the terrorists, or those who are either clearly insane or just after celebrity.
Hell the best two elected mayors the City's ever had were A/ An Orang-utan, and B/ A serial killer!
As for the Dark Judges, yeah they’re a bit one dimensional, but you could argue Ma-Ma was too, in fact a large proportion of movie villains aren’t exactly fully fleshed out. In many ways the Dark Judges are perfect for a film. Just enough character and a singular raison d'etre, crime is committed by the living, therefore kill all the living and crime ceases to exist. Add in the fact that they could look stunning if done right, and could actually be darkly humorous if handled correctly (Mainly just Death), and you have a great marketing tool—just imagine these guys on a poster?
Imagine the T-shirts, the action figures etc.
Of course the trouble is they aren’t characters you can throw into a first film. You have to understand the world of Dredd, and the role of the Judges, before you can then see the concept of Judges taking to the terrifying extreme. There’s also the problem that Dredd was a very grounded film, so you probably do need an intermediate film that introduces some more bizarre elements to the world, before you then take a jump off the deep end.
In an ideal world Dredd would have taken a ton of money and Dredd 2 would have probably featured the Cursed Earth, and introduced some supernatural or otherworldly elements. Dredd 3 would have then been about the Dark Judges.