I'm going to have to agree with the opinions I've heard from others; the Merlin books introduce a bunch of really nifty world elements, but the plot just isn't that good. Merlin spends a lot of time meandering about from crisis to crisis, and it's often hard to see how what he's doing relates to the overall story. And the Ghostwheel thing just seemed silly.
I still enjoyed it, and I'm still looking forward to playing in Amber some more, but I definitely preferred the first cycle.
Next up? I'm nearly finished with His Majesty's Dragon. That'll be a fun review to write.