I'm really enjoying The A.V. Club's Gateways to Geekery. They have more than 50 concise explanations of how to investigate topics that seem impenetrable.

The guides are both insightful and written well, here is a quote from their intro to emo:

More confusingly, virtually every good band associated with emo never identified with the label, not only because few artists like to identify with subgenres (especially ones with silly names—see also: chillwave), but also because emo’s sonic attributes have changed since the mid-’80s. What began closely aligned with melodic hardcore and punk morphed into more removed and moody sounds, then gradually grew poppier to the point that its only association with punk was power chords.