Yeah but even though Arnold's Conan might be off from some of the source material, it's still a fantastic movie regardless. Stallone's Dredd, on the other hand, is a terrible trash heap of a movie in general lol.
I think that even with it's faults, Dredd 3D manages to do what almost no R-rated remake manages to do in that it's a great film while still retaining the violence and brutality of the source material. Films like Conan, Total Recall, etc. (and I suspect RoboCop will fall into this) either A) get the violence right but screw up the story B) lose all the violence but kinda get the story right C) (and this is most common) dreadfully screw up both.
Dredd manages to get most (if not all) of it right IMO.