Volume 6 will be one of those books that you shouldn't judge by their cover.
Stain may look like a terribly overdesigned deranged ninja turtle, but it is what is inside that counts, right?
@Robby:
AssClass is so pun filled, jokey, and so Japanese though it'll have a hard time ever being a huge worldwide hit, regardless of how popular it is in Japan. And also, the author has been pretty adamant about it being an overall short series. Its still got another year or two in it, but it's not going to be a super long runner, and the anime staff knows it. (Which will still lead to it being a 5 or 6 year series total, for a 3 or 4 season anime, but its not going to run 10 or 15 years like the usual massive shonen breakouts.
And yet, Assassination Classroom is a worldwide hit. In France, a million of copies by the release of third volume. In Taiwan, public promotion and mainstream popularity (and a ban in mainland China). Even in USA, it made the first place on the New York Times chart. Certainly, it is a shorter work compared to many of its peers, but even with five years (if it does end next year) Assassination Classroom will have achieved as much as others would in 10 years.