Blogcritics.org reviews the Mysterians DVD. Overall, they weren't big fans. But apparently, they felt more Mogera would have made it a better film:
It's also a mystery to the film, seemingly defeated within the opening half hour, then making a barely noticeable appearance near the finale, only to be crushed by the armed forces machinery. It feels like it was added at the last moment, and that ends up being a significant piece of trivia. There should have been more scenes involving the robot, especially to break up the war involving a stationary dome.
Of course, most films could benefit from giant monsters and robots. But maybe that's just me.