The biggest thing the Arduino has brought for me is that it's extremely easy to work with, and versatile, + the the amount of users is huge!
To get a micro to control something like a LCD without that library for the Arduino would be a PITA.
Wiring up 9 LED's to a micro without pin headers would take ages, and be very delicate.
And you can do almost anything with it!
Being open source also adds to the awesomeness.