So the last book ended with Merlin being snatched up by a mysterious hand and dumped into Wonderland, and this is where Sign of Chaos picks up. Of course, turning to Lewis Carroll is a sure sign that the author had a "fuck it" moment, but Zelazny has an explanation at hand: Luke is on an acid trip, and since shadow walking takes you to the place of your desire, doing so on psychedelics can have colourful consequences. All well and good: the idea of characters being able to walk in shadow to the end of their imagination and no further was an interesting element in the first series, even though the author proceeded to ignore it as soon as he introduced it, so it stands to reason that shadow walking under the influence could take you to places you wouldn't otherwise visit, like a mad tea party.
But Luke being able to reach through shadow, grab Merlin in Amber of all places, and yank him to him? Such power was not allowed to any character thus far. Brand's job would have been a lot easier could he have simply grabbed Corwin and dragged him into the middle of a volcano. But it turns out Luke can do it just because he's high. Moreover, the author reveals that all the princes of Amber are aware of this, and have previously experimented with LSD themselves. Yet no one had thought to use this inconceivable power to destroy their enemies for, reasons.
While this is a particularly egregious example, this is a problem common to the series, and to the fantasy genre in general. Every time you introduce a new element into your setting you face continuity issues, as the reader will ask why this hadn't come up before, and will be very put off if it never comes up again. So the corner Zelazny has put himself in is that he is either committed to dedicated the rest of the series to drug induced antics, as that is a magical force nothing else compares to, or pretend this episode never happened and go on as before, thereby destroying what little connection with the setting the reader may have had left. The latter seems to be the author's modus operandi -- that's how he addressed psychic attacks via Trump, curses, eavesdropping, and whatever else, so we have to ask what was the payoff for all this? What did he gain by shitting all over the setting?
One of the most poorly executed Wonderland scenes I have come across, and I have seen Tom Waits' Alice.
So what are we left with, now that we've thrashed Amber yet again? Well, Merlin continues to remind us that he is an All American Boy who wears Levis and plays "football" and says things like "whatever" and "jeez". Luke is the cool kid who sunbathes and says "babe" and has a lot of sex and the author wants us desperately to like him, because he is so much smarter that everyone else. Two women from shadows are revealed to be much stronger sorcerers than just about anything Amber or Chaos can throw at them. The established cast of Amberites from the first series largely keeps backstage; they don't want to be part of this story either.