One-note characters, a plot that is nonstop coincidences, and gore galore. But wow, Burroughs does write some killer hooks--I could not stop reading.
Even the end is a hook--a massive story question is left dangling. Luckily, I had the trilogy-in-one book, so I read the prologue to book two, The Gods of Mars, to get the answer. And then stopped, because one was plenty.