I think if this was made in the 50s, story wise, it would be a great monster movie. it has a lot of juicy tidbits and campy action. While I agree that it's flawed, I think it has the kinds of flaws that I'm generally willing to over look in classic horror movies. It's sort of like Forbidden Planet for me. The over all idea, action, locations are fun enough that sloppy exposition, 2-dimensional characters and stilted pacing are not really problematic.
compared with other contemporary camp moster flicks (like mummy 3 for instance...) it was a blast to watch and appealed to every 12 year old fiber in my body while not offending too many of my more mature sensibilities.
on the other hand my girlfriend, who is a lot more demanding of movies than I am, was less than impressed.