What is the most under-rated comic event and why is it important?
Easy question, hard answer! Remember NOT your favorite just the most under-rated (or over-rated).
For me No Man’s Land established a map of Gotham, introduced Cassandra Cain, and changed many characters for years to come (ever heard of Harold Allnut?), yet few have heard of it.
Followed by the less biased (maybe favorites and most under-rated are the same sometimes!) Reign of the Superman which introduced everything from Superboy to the start of Zero Hour!