First of all, this is marketed as a YA book, but I think that is only because in the early 90's there wasn't much marketing distinction between YA and MG. This is NOT a YA book, it IS a MG. book. (The main character is only 12-years-old.)

The plot itself is pretty straightforward: kid is playing an alien shooter video game, the aliens surrender, and then the kid has to figure out how to get the alien fleet safely home while other players continue fighting. And it's got a lot of good points in there, with a lot of very pointed looks at real war (the Gulf War, aka Operation Desert Storm). It's short, and fun, and Johnny is a very relatable main character.

However. This was the early 1990s, and focused on young boys, and well. I spent as much time wincing as I did laughing. (Or more. Probably more.) Expect token diversity and fat jokes. The gender-based humor was Not Good. The "girls think they can play video games but can't" mentality might have been what boys thought at the time but I had thought Sir PTerry was above that. (I know the boys felt that way, though; I took great pleasure out of beating the guys in school at a game level they claimed was too hard.)

In my opinion, there's some fun stuff in here, but it really only needs to be read by Pratchett completionists.