Attack of the killer tomatoes is low-budget's answer to summer blockbuster Snakes on a Plane. Technically, it's the other way around, since AOTKT came first, but whatever. It's dumb, it has a small cult following, and you understand the plot when you read the title.
Tomatoes, you know, the kind in salads, attack people. This is shown in the movie, mostly as tomatoes being thrown at people with tomatoes on the ground everywhere. This continues for an entire movie, which might sound repetitive, but there's other side-tracks of the story as well, which more often than not are very funny.
The production values are non-existent but the filmmakers do their best to cover them up("I'm sorry, gentlemen, for the size of this room", the general says and then all the scientists climb over each other to get a seat) There are lots of silly plot points and many totally unnecessary, some funny and some not. Whenever it gets draggy, there's usually something really funny just in time. That's not bad.
If you need to have this told to you, then you will not like this movie, but I'll tell you anyway: Do NOT take this movie seriously. Enjoy the musical numbers, the stupid "Jaws"-like tomato attacks, the crazy characters, and all the other details that in then end makes AOTKT a fun experience.
