This is a long, complex book. It is an introduction, and unlike most introductions, it does an in-depth job of introducing the reader to the controversies in the field. The problem is that SLA is mostly problems, with very few concrete solutions. As such, the beginning reader is probably going to feel lost in the midst of a thousand competing theories. What is really important? Which ideas are winning, at least for now? Those are key questions that I would like to see answered. Some of the information was not as well organized as I thought and there was a lot of extraneous information. I didn't really notice until I tried to write summaries of the chapters. Wow! This book needs a nice, thorough rewrite. I feel like if the author were really disciplined and thoughtful, she could cut out 100-150 pages and this book would be a real gem.
Side Note: I thought it was strange that Gass kept setting up Krasher's view on input-centric language learning and knocking it down. His view was the only one that was treated in more than one chapter, and his was treated in at least 3! Strange.