Two completely different games, so it's hard to compare.
Dragon Age is a far more deep, complex, and rewarding experience if you have the time to drop into it.
With that said, I quite enjoyed Fable 2 - played it to the end and beyond. It was one of my favs for that year. I couldn't finish Dragon Age (on PC)... too epic.
I'm a casual rpg-er, so take that for what it's worth.