The Guns of Avalon (1972) continues the story begun in Nine Princes of Amber. Lord Corwin is free, ready to follow his revenge against Eric. All he has to do is return to Avalon, and on that hangs a tale, for strange and terrible things now come out of darkness everywhere, including at Amber itself.
If you didn't know that this story was essentially a serial, now you do. Although the books cover distinct episodes, and could stand alone, its stands far better together with its peers. Our enemy has bee introduced in our power fantasy, and that enemy is anybody else. If you will, if this was a business power fantasy, the enemy would be the competition, the only thing more fearful than your co-workers.
The story reads mildly more polished than the first book, but contains few literary sensibilities. This is not the kind of book you read if you want beautiful writing. Zelazny's prose is all business, getting done what it needs to get done, sometimes effectively, and at other times, with all the ugliness of a car wreck. The book was written in one draft, possibly two, containing all the flaws that you would expect to get from fast drafting.
As the story is a serial, it moves at a different pace than a more traditional work. It answers some questions, raises others, leaving you with an ending that is indeterminate rather than satisfying. Its power comes from the unfolding of evens, and the continuous downward cycle of the situation in Amber. Everything gets more complex, but never for the right reasons.
As for all its flaws, it contains many. They will either alienate you or refuse to stop you. I can't see someone being lukewarm to this book. It follows what came before, for all its blessings and curses.