The primary draw of the books is Geralt himself, who remains one of the better written protagonists of fantasy I've read over the years. He is a cold-blooded but surprisingly decent mutant created by a secretive order of killers called the Witchers. Long ago, they were necessary to protect the human race from monsters but they've mostly been killed off and the immortal mutants no longer have a purpose in life.
"The Voice of Reason" is the framing device of Geralt having been injured (in the second story) but is recovering in a Temple of Melitele. The head priestess Nenneke makes him recount several of his adventures. It's not a bad framing device but could have been left behind without losing anything.
"The Witcher" introduces Geralt as a Man with No Name-esque badass who is hated on sight. However, the King of Temeria has his incestuous daughter has been cursed to become a monster. Geralt knows the only way the curse can be broken is if he can capture it and stay beside it until morning. It is a heavily action-based story and extremely entertaining.
"A Grain of Truth" is a retelling of Beauty and the Beast where the Prince actually was a monster before his curse but has had his disposition improved by it. We also discover Beauty isn't the best sort of person for it either. Geralt is surprisingly pleasant to this Beast as well, despite the man's many many crimes.
"The Lesser Evil" is another fractured fairy tale with Geralt falling in love with Snow White the Bandit. She has seven dwarves and they murder people for money. They also murder people because Snow White is wanted for her part in a prophecy which may be, even in a world of magic, complete nonsense. I think this is easily my favorite of the stories in the novel.
"A Question of Price" is the origin of Ciri, the deuteragonist of the Witcher Saga, though she's not yet born by the end of the story. Basically, Geralt is called in as part of a complicated marriage compact which has already completely gone to hell by the time he arrives. We also meet Pavata, an impressive character who is able to stand toe-to-toe with Geralt. The fact Geralt isn't trying to be anything but respectful just makes it all the funnier.
"The Edge of the World" is my least favorite of the books as it involves Geralt and his friend Dandelion getting captured by some elves with too high of an opinion of themselves. The peasants are shown to be complete idiots too.
"The Last Wish" is the titular story of the collection and extremely entertaining. It introduces Yennefer, Geralt's love interest as well as partner, who is one of the better written female characters in fantasy. The fact she's someone who utterly steamrolls Geralt as well as those around him only to get back plenty in return makes her a constant source of amusement.
In short, this is a great bunch of fantasy stories even if I was a bit nonplussed by their fractured fairy-tale nature. They do, however, have an incredible main character as well as a well-developed supporting cast and mythology. I recommend fans of the game and fantasy fans in general all check out this work because it's one of the better buys you'll probably get out of a translated work.