Good old slightly campy fun! I wouldn't class Lyrec as one of the most literarily exciting fantasies I've ever read, but it is exactly what I look for when I go reading fantasy from the 80s--solid prose and a story that is more enjoyable than anything else. Obviously it doesn't exist in a vaccuum, I think that the novel has some things it clearly values (connection and friendship among them), but it is first and foremost a good yarn. Tonally it reminds me of Michael Moorcock's Hawkmoon books (not so much the ones about Corum, not that melancholy) even though it was published a good fifteen years after the end of The History of the Runestaff. (It's also less anarchist, but that's sort of what I mean about not existing in a vaccuum--I think there is a politics under Frost's novel just like there is under Moorcock's and I don't think its too anathema to me, or I wouldn't have liked the book, but it isn't the dominant presence on some level.)
The worldbuilding feels a bit haphazard in places--Frost isn't interested in providing detailed explanations of why how/why everything about the world works or came to be--but in the end every important worldbuilding element does serve the story, sometimes in really unexpected and clever ways. The plot is an exciting adventure tale--Lyrec, a traveller from another world (not that the story takes place on our world, just a world like ours) is, with his friend Borregad, in search of his lost lady and the evil Miradomon who destroyed his home planet and is on a multi-world rampage to garner power. Lyrec is nicely characterized, as is Borregard--I love their friendship and their conversation. Most of the rest of the cast are pretty solidly supporting characters (except for Miradomon, who is a marvelously evil villain), but they still largely move beyond just being paper cutouts and setdressing.
The one concern with the plot is that it takes a few chapters before you have enought pieces to start understanding how the different threads of the story you've been jumping between fit together, but if you have the time to just keep reading for the first several chapters once you start, that will help enormously. All in all recommended for a relatively lighthearted read.