This is a movie from the early days of the science-fiction genre, in which aliens come to Earth to either conquer or just destroy us. The type of movie that perhaps is also being more of the monster horror sort and features flying saucers on string, fake looking studio sets, people in rubber suits and wooden acting performances. Yes, this movie also has it all but still I rate it to be a slightly above average one, since if features a pretty decent story in it.
To be completely honest, none of these movies within this particular genre are great ones, not even the most classic ones, with the exception of just a few. But still these type of movies were and still are quite popular to watch. It's perhaps because they always play on our fears (remember, most of these movies got made during the height of the cold war period), feature an heroic main character that saves our world, or perhaps it's just simply because they are movies with a certain charm to them.
This movie features all of the typical genre elements but the movie takes some good approaches with its story. It chooses to be not action packed or scary really. It tries to do more with its mystery elements, which makes this a pretty effective thriller.
It's definitely not the most exciting movie to watch, so I can understand some people end up not liking this movie at all. However if you like, lets say, "Invasion of the Body Snatchers" or "The Thing from Another World" type of movies and stories, this movie might very well be worth your time.