This is an experiment for Planet Stories, two 70-80 page novellas by different authors in the manner of an old Ace Double. Does it work? Well, only insofar as the stories are any good. One is, and one is..not so good.
As a 15 or 16 year old, Michael Moorcock wrote some Sojan short stories for a fanzine. This is a collection of those stories, apparently somewhat revised. It's not great - the characters are less than one-dimensional, the narration inconsistent, and the setting contradictory - in the space of a few pages Sojan refers to his boss as "War-King" and "Emporer", and implies both hereditary succession and election to the position. Each 2-3 page chapter is almost a standalone story.
For a brief while, it rises above itself when Sojan crosses the Demon Sea and confronts the evil priests of Rhan and the Old Ones. This pretty obviously draws heavily from work of H P Lovecraft, and then Robert E Howard's Tower of the Elephant Conan tale.
In the introduction to the book, Erik Mona points out that Moorcock's first thoughts on republishing Sojan were that it would be a mistake. I would say that Moorcock should have followed his initial instinct and let this stuff fade into obscurity, or rewritten it to a much greater degree than he did.
Under the Warrior Star is the better story of the two, for all that follows the "sword & planet" formula - set out by Mona in his introduction - precisely. Brax is a modern Earthman who stumbles across a secret Government facility in the wilds of Alaska and becomes a human guinea pig to be sent into an experimental man made universe. There is a planet there, which is both strangely Earthlike and strangely not (for instance, the Earth is actually a giant tree). While there he inexplicably gains superhuman speed and strength, meets fellow more or less men, and of course, a woman (in a chapter helpfully titled "The Woman").
There is then an adversary to overcome: The One, an odious plant hive mind that has giants for slaves and captures and devours humans. Brax uses his unique Earthly knowledge to good effect, and heads off to the inevitable confrontation...and I'll stop there, so as to avoid spoilers.
Yes, the story is formulaic, but the telling is good and has a few wrinkles: rather than try to explain everything, the first person narrator sometimes just shrugs and says "I don't know". This works better than getting bogged down in detailed mumbo-jumbo, and lets the plot and action continue. The story does not raise issues of existential angst: it just offers a few hours of escapist reading pleasure.