Maybe you can tell from my background image that I’m a big Arduino fan.
Just look at it, its gorgeous! All those beautiful input/outputs! USB connectivity! A reset button if all goes wrong!
Well, ok, enough fanboy enthusiasm. I think that the biggest reasons why the Arduino boards are so popular are the contributions of the sizable Arduino community and the well developed IDE (Integrated Development Environment).
When I got my Uno board last year, I quickly blew through the example programs and set out to write the programs that I was interested in. The forums were very helpful as I muddled through my first few newbie challenges.
The IDE is so easy to use. It takes care of all of the code verification, compiling, communications. And the Arduino flavor of C code isn’t very hard to learn.
I know of no other micro controller board that is so painless to get started with, and I think that’s the single most important qualification for widespread adoption, even for non-engineering types.
Arduino was easy to pick up, and now I can’t put it down.