Book Reader has over 10 thousand audio books. All of them are in public domain, recorded by volunteers for free.
Hence, naturally each book has a different experience in terms of reading quality, speed and overall feel. And with so many books to choose from, it can be hard to find a starting point.
In this article, I list down some of the most interesting books that you could play over Book Reader. The listening list is a mix of some really good books, some really great recordings and some books which are simply classics.

To play any of these books over your google assistant, simply connect to the Book Reader app by saying:

Ok Google, talk to Book reader  and then say  Play <book_name>

Mysterious Island by Jules Verne Read by: Mark F. Smith
Four Civil War castaways find themselves stranded on a deserted island.
But, while they may have no boat, no plane, and no motor car, they DO have plenty of Yankee ingenuity, and proceed to turn the island into a well equipped and
prosperous little community!  
Play Mysterious Island

The Prisoner of Zenda by Anthony Hope Read by:Andy Minter  
An English gentleman has to fill in when his distant cousin, the king of a small European country, is taken prisoner.
Woods, moated castles, pomp, swordplay, gallantry, villainy and a beautiful princess. What story could ask for more?  
Play The Prisoner of Zenda

Pollyanna by Eleanor H. Porter Read by: Mary Anderson  
A VERY good book about how to have a great attitude no matter what circumstances you find yourself in. (Skip the sequel though, it stinks!)  
Play Pollyanna

A little Princess by Frances Hodgson Burnett Read by: Kara Shallenberg  
A young rich girl loses her father, and all of her money. She finds herself moving from the favorite student at her girls school to the lowest servant. BUT, no matter what happens to her, she is always a princess on the inside.    
Play A little Princess

King Solomon's Mines by H. Rider Haggard Read by: John Nicholson  
A prince, A lost kingdom, fabulous wealth, and Alan Quatermain, the penultimate African explorer and adventurer!  
Play King Solomon's Mines

Star Born by Andre Norton Read by: Mark F. Smith  
A human colony in another galaxy where the humans have made friends with the local mermen. But now NEW humans have arrived on the planet, are they a threat, or hope?  
Play Star Born

Plague Ship by Andre Norton Read by: Mark Nelson  
Space trader Solar Queen has trouble cementing it's claims with a new planet, AND dealing with a strange disease they pick up there.    
Play Plague Ship

Star Surgeon by Edward Nourse Read by: Scott D. Farquhar  
Dal Timgar is the first non-human to study medicine on Hospital Earth, can he overcome prejudice, solve a medical puzzle, and earn the Silver Star of a Star Surgeon?  
Play Star Surgeon

The Colors Of Space by Marion Zimmer Bradley Read by: Mark Nelson  
Can humans steal the secret of the star drive from the alien Lhari?  
Play Colors Of Space

Badge of Infamy by Lester Del Ray Read by: Steven H. Wilson  
A doctor who's lost his license tries to practice medicine on Mars.  
Play Badge of Infamy

The Pilgrim's Progress by John Bunyan Read by: Joy Chan  
The 17th century classic Christian allegory. Pilgrim makes a journey from the city destruction to the celestial city!  
Play Pilgrim's Progress

Fighting The Whales by Ballantyne Read by: Lee Elliott  
A fascinating look at what it was really like to be on a whaler. One is left with the impression that hunting and catching a whale in a sailing ship was akin to you or me being stalked, ambushed, and killed by a shoebox full of mice.  
Play Fighting The Whales

Around the World in Seventy Two Days, by Nellie Bly Read by: Mary Reagan  
True story of a woman journalist who decides to beat the fictional Phileas Fogg with a REAL record breaking trip around the globe.  
Play Around the World in Seventy Two Days

The Jungle Book by Rudyard Kipling Read by: Meredith Hughes  
The story of Mowgli is here, but also one of my absolute favorites, Riki-Tiki-Tavi!!!!  
Play Jungle Book

Cinderella by  George Calderon  
Set on a "bleak and cheerless heath overlooking the fjord" we meet Ibsenesque heroine Mrs. Inquest, her step-daughter Hilda, and her daughter Hedda, who is engaged to be married to the unfortunate Tesman. Thus begins Calderon's hilarious Ibsenesque version of Cinderella  
Play Cinderella

Penrod by Booth TARKINGTON Read by: Jonathan Burchard  
Join Penrod Schofield and his wistful dog Duke, in a hilarious romp through turn of the century Indianapolis, chronicling his life, loves, and mostly the trouble he gets into.    
Play Penrod

Bunker Bean by Harry Leon WILSON Read by: Joseph Tabler  
Young, self conscious, timid stenographer for a New York businessman with a beautiful daughter (the flapper). He emulates stronger types, but not them. He grows up in this humorous volume from 1913.  
Play Bunker Bean

The Enchanted April by Elizabeth von ARNIM Read by: Diana Kiesners  
A recipe for happiness: four women, one medieval Italian castle, plenty of wisteria, and solitude as needed.  
Play Enchanted April

PS: Special thanks to u/Kilarin for sharing her recommended list