I don't consider it a "must read" but it is worthwhile. Definitely agree with Pastor E below that studying "radical" and then "Radical Together" back-to-back would maximize the experience. The books are a good reminder of how far the American church has moved from the biblical model of church gatherings. You'll certainly be challenged to THINK if nothing else! If you're going to do a small group study, I'd recommend (at least for group leaders) checking out Platt's original sermon series. You can find full length video and audio files, sermon notes, and small group material at http://www.brookhills.org/media/series/radical. If you're going to do it as a youth group study, invest the time to really dig deep!