Part 1. They are examples of "purple prose." The reviewer is using almost poetic language to convey strong feeling. "From the California high desert to a Texas prison yard, from Ozarks dive bars to the shadows of Hollywood"--He's writing about crime and the underworld. You will get to learn about places you would not learn about in any other way. "these stories burst with gutter grandeur and criminal mythology." "The gutter" is an idiom for the criminal life, low society, city slums. (From the days before sewers, when human waste was dumped into gutters). It is surprising to hear the word "gutter" followed by "grandeur." It means that the book romanticizes the criminal life and makes it sound grand, like the lives of kings and queens. "Harper burns through prison-tatted flesh"--"tatted" means "with a tattoo." I think "prison-tatted" must mean an amateur tattoo made in a prison in some crude way, rather than professionally with ink and a tattoo needle. It means "this writer REALLY knows about prison life and criminals and is writing about the toughest of them." "to expose his characters’ hardened, scarred but still beating hearts." They really are hardened criminals but they are human beings too and you will emphasize with them and care about them.

Part 3. "A harrowing, hallowing ode..." The reviewer wants us to think that he, too, is a "virtuoso" and is showing off! "Harrowing" and "Hallowing" are alliterative. "Harrowing" means it will worry you. "Hallowing" means it will make you holy, uplift you. And an "ode" is a piece of literary poetry. Shelley wrote a famous poem, "Ode to a Skylark," but Harper writes odes to... "those whose options boil down to a bullet, a bank, or a strange stretch of highway." I.e. criminals. Bank robbers. More alliteration, "Boil," "bullet," "bank," and then "strange" and "stretch," and back to the H's with "highway." "American Letters..." means "serious literature "...has found in Harper an agent worthy to take the crime fiction tradition into the 21st century.” He's saying Harper is one of the greats. In the same category as Raymond Chandler and Dashiell Hammett, who wrote commercial (money-making) crime fiction that is, nevertheless, taken seriously today as literature.

Part 2. "He does it with a virtuoso prose style"--"Virtuoso" usually means a musician. A violin virtuoso is so skilled that he can make sounds with a violin that less-skilled players can't make. He's saying the writer is like that with words. "that mixes pulp panache"--Magazines are classified as "slicks" and "pulps." Slicks are high-class magazines printed on shiny paper. Pulps are smaller, about A5 size, printed on newsprint. Magazines of "genre" stories--detective stories, science-fiction--are "pulps." In the 1930s and 1940s, there were a lot of pulp magazines that printed crime fiction. "Pulp fiction" has come to mean "hard-boiled crime fiction for a less educated audience." "Panache" is a very literary word. Just as he surprises us with the phrase "gutter grandeur," he surprises us with "pulp panache." "literary flare"--I suspect that's a typo for "literary FLAIR". It means skill and style "pure nitroglycerin." It is very exciting. It has many scenes in it that "explode." I suspect this is a way of saying that there is lots of violence. He's saying that this writer a) writes about crime and violence in a very detailed, realistic way, but also b) is a good writer who uses words skillfully.