Typos.
That's all. There are lots of them, and they bug me.
Other than that, I love Gardner's work. The pacing is great, the perspectives are varied and believable. The wit and humor - far more prevalent in the proper League of Peoples books - still shows through most of these stories.
But for the Kindle edition... It needs a good once over by an editor to fix some things. These errors look like the book was scanned, read for major issues, and pushed out. I don't know if the print versions share this problem, but the kindle edition is a major disappointment (because I get caught up in these kind of things).