I can't say for sure what made Awakening so successful, but here's my story:
Before Awakening, Fire Emblem was always a series that I wanted to get into, but never could for a lot of reasons. I loved Advance Wars since the GBA days and when I found out that Intelligent Systems made Fire Emblem too it seemed like a sure bet I'd enjoy that series as well. So I tried a couple of FE games, like Path of Radiance and the GBA Fire Emblem, but it never enthralled me the same way Advance Wars did. The pacing was too slow and the battles seemed to take forever due to the poorly executed and unnecessary battle scenes. The story at times seemed to take itself too seriously for my taste, and the characters were boring and lacked personality. I found it hard to believe that Fire Emblem and Advance Wars could be made by the same developer. Their approach to strategy games was just too different.
Then Awakening came along and changed everything. Of course, the first thing that caught my attention was the art. I am a big fan of Yusuke Kozaki's work, and I found Awakening to be some of his best. Once the demo was released, I decided to give it a shot, because, why not? To my surprise, it seemed like every complaint I'd had about the series before had been addressed. The combat was quick and smooth. The battle scenes allowed us to control the camera, adding just enough interactivity to keep them from becoming obnoxious and repetitive. Even the area where I had no complaint before had been improved: the music. I loved the soundtrack. And then the characters. Expressive portraits accompanied the dialogue, which was funny and always amusing for its playfulness and ability to catch you off guard. And that's what really left a lasting impression on me. After all, they'd just be pawns on a chessboard if not for their interesting back stories and personalities.
After spending over a hundred hours playing Awakening and still not seeing all there is to see, I can easily say that it has outranked the original Advance Wars as my favorite Intelligent Systems strategy game. I only hope they can revitalize the Advance Wars series in the same way in time for its next release.