I was shopping online for microphones today -- reading reviews, checking prices, etc. One of the best things I ran across in my research was Ty Ford's helpful website. On it, there are a number of reviews and tutorials. One of the best videos on his site is a comparison of four different mics, which does a nice job of explaining the difference between shotgun and hypercardioid microphones.
The movie takes a little while to load, so be patient. And wear headphones. Without them, the nuances of the differences between microphones will be lost...and nuances are what this is all about.