The first thing you should look at is the new system. It is essentially magic that refreshes per encounter and puts some rather powerful effects into the hands of fighting characters. If you are familiar with the almost supernatural martial arts abilities that can often be found in Chinese wuxia movies and literature (Think Crouching Tiger, Hidden Dragon and Hero), the new system has a similar flavor. I happen to think it's one of the most interesting and fun systems I've seen in years, but I can see why it might not appeal to everyone.
Next, have a look at the three main schools that the crusader will be drawing most of his maneuvers and stances from: Devoted Spirit, Stone Dragon and White Raven. Devoted Spirit has maneuvers that can deal or heal significant amounts of damage. White Raven has maneuvers that buff allies or create openings for them to exploit. Stone Dragon has moderately good offensive and defensive abilities, but some of its higher-level meneuvers can be quite devastating. The question to be asked here is whether you are OK with the character being potentially (though not reliably) able to produce the effect in question at (2 x maneuver level - 1) level once every four or so rounds per encounter (three or so rounds with the right feat).
Finally, have a look at the crusader class itself. The main pain with the crusader is that its maneuvers are randomly granted at the start of combat, and a new maneuver is randomly granted each round after that. Unless you make use of cards to keep track of which maneuvers are granted and used (a method suggested by the book), it can get very messy.
Allow yourself a few days to a week to fully digest the material in the book. If possible, borrow it off your player before making a decision. If you're running a game in the interim, you might allow him to run the character during that session as a trial before you make your final decision (but do not use this as a substitute for reading the book).
Hope it works out for you and your group.