I'm a fan (and you should be too) because...BECAUSE THEY ARE THE BEST IN THE WORLD!
The songs are greats, the videos are fabulous, messages are special and the band are amazing! 
I admit: the first time I heard them was in the game svr 2007 ... yeah that's right!
From the first second I loved the songs, especially "Animal I Have Become"... I searched in youtube to see more musics and I heard the "Pain" and I loved ... then I heard the others and sincerely said to myself: "humm I don't like very much" ... it was at that time ... now I got the musics and i know the lyrics by heart!
Then I tried to know more about the band and I just admire adam ... is something I can not explain very well ... is one of the reasons of my existence ... when I feel down seems like the lyrics understand me ... is amazing ...
...I am fan because I love the three days grace and I admire very much adam =) ...
(sorry my english ;P)