Karma, by Ostlere, has a Lexile of 400. It's a wonderfully complex book, full of imagery and allusions. It's also written in diary format with free verse and sentence fragments. The small number of words on each page evidently give it the low Lexile number.
In short, no reading level scheme is perfect. The ones that appear best for my use, are those that use a variety of measures, including vocabulary, complexity of sentence structure, and aspects of comprehension. When my kids were younger, Fountas and Pinnel and DRA levels were most useful. Once they each hit ~4th or 5th grade level, it doesn't seem to matter as much.
When it comes to assessing a reading level for school, reading levels sometimes appear random, as they can be so sensitive to subjective judgement from the teacher and from one text to the next. We've found that progress assessed by one teacher through a year is reasonable feedback. Correlating scores across years is problematic, particularly when disabilities are considered (e.g., DS has a speech disability that affects his oral reading accuracy and rate.)
