A critical issue.

Eh, well, it's not quite defined that way; everything is subjective for everyone. In short, for a beginner there are about a dozen titles you can check out (by choosing an interesting genre) and only then draw a conclusion as to whether it's worth continuing; like, say, Death Note, Fullmetal Alchemist, Hellsing, Berserk, Naruto, etc. Basically, things you might have heard of even without getting into the subject.