Actually not awful
I've heard for ages about how hilariously bad this movie is, but when I finally watched it, I found myself getting into it.
The biggest problem in this movie is near the beginning, when the kid gets knocked out, and we're suddenly treated to footage of lizards ('dinosaurs') fighting for several minutes (this is probably supposed to have been inspired by his conversation with the archaeologists), without explanation. But once you get past that, it starts making sense - sort-of.
For me, Robot Monster is like a weird dream, which makes sense since *SPOILER* it turns out that it is a dream. The limited locations and illogical characterisations make a lot more sense from this viewpoint.
Also: the acting, for its day, is not particularly bad; the Leonard Bernstein music enhances the mood; and Ro-Man just looks so cool!
I think if you take it as a kids' movie that's supposed to seem like a dream, and get into the old-fashioned feel of it, Robot Monster is worth watching.
Now, flame me.