There are many things that make a great book. They all have to converge correctly togehter in just the right balance to create great works. The three most important elements in my opinon are strong characters, expressive writing and a great or inventive plot line.

Strong characters are a definate must. You have to creat characters that your reader can identify with and will want to read about. These people need to have either outstanding qualities or dispicable ones. There needs to be something unique but familiar about your characters. Most main characters are easy to type. You have hero, villians, damsels in distress,etc. but the great characters are more than just the position that they fill. They have dpeth and something that makes them memorable. There are still to this day some characters that I first met when I was a child who still hold my interest because of their personality. These characters have to become real to the reader. For example one of the reasons that Harry Potter and the Twilight series have done so well is because of their strong characters (not that I would consider them great works mind you but they do have the character bit down).

Expressive writing is also important. The words on the page need to come alive to reader. There needs to be a tricky balance that allows the read to 'see' what you are describing while still eaving enough to the imagination that people can allow their imaginations to run wild. You need to vary your writing structure and create a unique voice for each of your characters. A great book's writing style is memorable. After reading in it for any length of time you find yourself prefering the voice of the author to your own and begin to speak with a bit of their style for a short time. Expressive writing allows peopel to escape into the created world.

Inovative plots are also necessary. You need to come up with a story line that is unique and has never been seen before in quite this way instead of trying to palely imitate the geat writers of days gone by. I don't know how many times I get tired of reading another desguised version of Jane Eyre or The Prince and the Pauper. A great books takes a new spin on things or tells a story rarely or never told before.

I hope this give you an idea of what great writing is and what to look for when reading or writing yourself.