If you are a fan of the X-men comic book then this is truly required reading. First off, make sure you are reasonably up to date with the main X story arcs of the last few years, namely House of M, Decimation, Deadly Genesis and Endangered Species otherwise you are going to have a real problem in following most of the action. While I readily admit that Messiah Complex is by no means perfect, it is most definately the best Marvel crossover in a long time, with most story arcs fitting together quite neatly. This book is also important as it marks the moment when the X-groups are no longer Xaviers responsibility and become Cyclop's X-men.