I expected it to be dumb, but it was actually a very enjoyable old movie. Because of the age of course there are some corny individual parts, you can't avoid that, but the movie as a whole was in fact quite good. I was pleasantly surprised, and I legitimately enjoyed it for what it was when I had expected I would have to enjoy it through a lens of remembering when it was made.
One thing that made it cool was that it used actual historic elements from the Cold War in its story like the arctic radar fences and the civilian ground observer corps.
Also, with the monster being a mantis it just inherently had some really cool imagery, like when a soldier tried to fight it with a flamethrower and when it was in a dogfight with a squadron of fighter planes.
And it had what I think, in all sincerity, is one of the greatest scenes ever in cinema: A giant praying mantis crawling up the Washington Monument. Just look at this: