Problem number two is the plot. It's the year 3000, and the earth is occupied by unpleasant aliens called Psychlos. The human race has been reduced to a slave-species of 'man-animals', and the cities are in ruins. Not a problem in itself, except for the fact that during the film, several of these cavemen learn to fly military aircraft that have been lying dormant (and, I guess, fuelled) for 1000 years. OK, granted, the lead caveman has been taught the Psychlo's language and earth's history by a 'learning machine', so I suppose he could do it. But his friends learn in a flight simulator that has been sitting there ready to go for the last millennium. These people are cavemen. They have no comprehension of technology. They wouldn't know how to open the door of a flight simulator. It probably has a code-lock on it anyway.
Problem number three: Even if a nuclear device were to ignite a planet's atmosphere, I don't think the planet would physically explode.
The above problems are enough to ruin a film for me. However, if you can ignore them, then there are a few things worth seeing the film for. Among them are the make-up and costume design, which I thought were brilliant. The Psychlos are really the most disgusting creatures I've even seen in any film, and I just hope they were meant to be. The special effects are quite good too; I especially liked the Psychlo spaceships which had excellent heat turbulence effects. The learning machine is really cool as well (I could do with one of those to learn Finnish) and John Travolta is excellent, even under all that make-up.
In a nutshell, though, Battlefield Earth isn't worth the time it takes to watch it; not even if you're in the mood for a good laugh.