To identify the characteristics of a good fantasy novel, start with the plot. A good plot should be both exciting and logical. It should not have too many holes or Deus ex Machina moments. Consider the language used. Beautiful and descriptive language can enhance the reading experience, as seen in the works of Ursula K. Le Guin. Additionally, the presence of unique and interesting concepts, such as time - traveling in 'The Time Traveler's Wife' (which has some fantasy elements), can be a characteristic of a good fantasy novel.
Look at the world - building. If it's detailed and immersive, it's a good sign. For example, in 'Mistborn' by Brandon Sanderson, the world has a unique system of magic based on metals. Also, check the characters. Are they multi - dimensional? If they have flaws and growth, it's likely a good fantasy novel. Like Eragon in 'Eragon' who starts as a farm boy and becomes a dragon rider with many challenges along the way.