A quickie sequel to 1957's Amazing Colossal Man, War of the Colossal Beast is an utter disaster not only as a sequel, but as a stand-alone film. The prequel had some interesting ideas dealing with the idea of a decent man with a huge (pun intended) problem. The sequel throws all of that out for a cheap cash-in during the monster-on-the-loose era.
With an extended flashback sequence, Colossal Beast barely breaks the hour mark. Oversized 60-foot tall Colonel Glenn Manning returns after being shot with a bazooka and falling 700 feet at the end of the previous film, only now with a disgusting facial deformation. He also went through a slight personality change, forgetting the basics of language and speaking in nothing more than loud grunting. The make-up is obvious, and it's hard to believe that's the worst that happened to him after the battle in the original.
Instead of destroying, rampaging, and generally being a nuisance, most of the movie has the Colossal one tied up inside an airplane hangar. There's an amusing sequence in which government officials (all with signs on their desk saying what their department is) pass around the burden of dealing with the problem via phone conversations until it ends up in a circle of "call this person." It's one of the few highlights.
In fact, it's hard to take this as a separate film. Combined with the previous one, it would lose the extended flashback sequence and feel more appropriate. As it stands, the weak special effects (you can clearly see right through Manning in a few shots), thin, barely existent plot, and cheesy miniatures do nothing to warrant this movie's existence.
As an odd bit of trivia, the final 30 seconds or so of the film are in color. Snipping color is an easy way to save on the budget, but the sudden, jarring change-over is completely useless. It takes away from what could possibly be the film's only dramatic moment.