Take good old-fashioned space opera:
Add cheese, lots and lots of cheese:
Mix well and serve. What is the result? The Star Kings by Edmond Hamilton.
John Gordon recently came back from a war (the book was published in 1949; I will leave it to you to figure out which war). He is trying to fit into a quiet life of an insurance company employee and does not have too much success of it. The voices in his head at night do not help any.
Not much later it turns out the voices are real: a scientist from very remote future named Zarth Arn tries to make a contact with Gordon. I am talking about very
remote future - hold on to your heads - 200,000 years. I will spell it for you: two hundred thousand years. Zarth Arn told Gordon he devised a method to swap minds across the time and space and he is very curious to see what such remote past looked like. If Gordon agrees he in turn will see the future.
The majority of people I could think of would jump at the opportunity: the procedure is safe, reversible, and temporary. So Gordon wakes up in the body of Zarth Arn in his laboratory in a remote location on Earth. He did not even have enough time to learn the basics of life - like language - as things turned out terribly wrong
and he is whisked on the other side of the galaxy away from the unique mind-swapping equipment with little of ever get his hands on it. Basically he is stuck in a stranger's body in completely unfamiliar surroundings.
This book has everything a pulpy cheesy space opera is supposed to have: a Galactic Empire, Dark Forces trying to control it, a beautiful princess, epic space battles, strange alien worlds. If you think it sounds familiar: so did I which prompted me to check the publication date. This book predates Star Wars by almost 30 years and it is quite possible it was one of the inspirations for George Lucas.
On the positive side it was an easy read and good enough to make me put the second book of the duology on my to-read shelf. Gordon is not a superman who can fix the future problems using his brute strength or wits. The main idea of the book is not about it; it is more about accepting the responsibility and acting on it. To my complete surprise The Big Bad guy showed some signs of humanity by the end of the novel - enough to say he was not a stereotypical bad guy.
On the negative side the cheese was aplenty in the writing and dialog. I also found the writing to be somewhat clumsy occasionally. Because of this two reasons I really cannot give this book 4 stars and keep a straight face. 3 stars it is, but I gave 3 stars to more boring and worse books before.