Physicist Dennis Nuel is the first human to probe the strange realms called anomaly worlds: alternate universes where the laws of science are unpredictably changed. But the world Dennis discovers seems almost like our own—with one perplexing difference. To his astonishment, he’s hailed as a wizard, meets a beautiful woman with strange powers, and finds himself fighting a mysterious warlord as he struggles to solve the riddle of this baffling world.
While this novel is couched as sci-fi, it reads like fantasy. Sure, the beginning of the novel takes place in a near future Earth, and there's the zievatron thingee that allows Nuel to travel to another world, but it ends there. The rest of the novel is spent in a medieval world, and Nuel must put his wits to use inventing things to gain favor and the upper hand in his struggles with the denizens of this world. There's a princess who needs rescuing, castles and dungeons, and superstitious peasants.
So what is "the practice effect?" Well, you know how you have to practice playing the clarinet to learn a song or get on the ice and skate to improve your hockey skills (maybe not the best examples, but you should get my point)? On this world, that's how you make objects better. The more you use them as they're intended, the better they get. Got a pair of ripped jeans? Wear them a lot and let them practice being jeans and those rips will go away. Got a crude stone axe? Go chop some wood with it, and it'll slowly sharpen on its own accord.
If you remember physics class, you'll know which law has been turned on its head to make worn out things magically like new. Just another element to bolster the case for this being a fantasy novel.
90+% of the story is told from Nuel's POV. Fortunately that 10% exists as it affords the reader a chance to learn that the villainous Baron and Princess Linnora aren't two-dimensional stock characters. The Baron is greedy and lusts for power, but he does have a few principles. It was especially nice to see that, while the princess was in need of rescuing, she carried her own weight as the novel wore on.
None of this is said to infer that this is a bad book. It's definitely not. I enjoyed it. The pacing is good, and the story is entertaining. The characters are fine, though they could've used a little more depth. They're likable, you still root for them to succeed. The story could've devolved into one of those stereotypical square-jawed male heroic fantasy tropes that were so popular decades ago, but it didn't. Not Brin's best work, but still fun.