There was no need for a sequel. The original movie's entire purpose masked a parody of Hitler's Nazi youth recruitment campaign.
The "bugs" resembled the "Jews", and so on and so forth. The television ad campains were similar to that ran by Hitler, encouraging youth to fight, because the Jews were a disease.
Also take note of the shower scene, Dina Meyer in particular, all the recruits were in extremely good physical condition, which played towards Hitler's being particular to the perfect human body.
Doogie Howser's Gestapo uniform at the end of the movie would have sealed the deal for anyone who hadn't caught on earlier.
Like I said, if the sequel lacked any of these qualities, it's just another Sci Fi movies.
I'm telling you all this movie is almost as bad as leperchaun in space. I mean you have the same kind of special effects, camera lighting, and non existant story. The movie is so terribly bad. They couldnt afford to do the bugs, so they took shots from the original, or they would just keep reusing the same camera shots of the bugs running twords people and cut to a close up of someone firing a gun.