To put it simply, if you like Baldurs Gate, Icewind Dale, Neverwinter Nights, those games on the PC, then Dragon Age is for you. Its got a much darker storyline than those, not to mention a more original back story and lore.
Bad Company 2 looks beastly though to be honest, but I have games...
Not necessarily. Other exclusive titles that sold quiiiite a few, like Left 4 Dead, Mass Effect, back when Oblivion was exclusive it sold over 4 million, all those titles sold plenty. That's not saying that PS3 titles don't sell, Uncharted, Metal Gear Solid, and Resistance have all sold over 4...
All of my information is taken from VGChartz, which compiles numbers taken straight from developers.
Xbox 360 Release Date: November 22, 2005
PS3 Release Date: November 11, 2006
Xbox 360 Total Sales: 35.11m
PS3 Total Sales: 29.01m
Xbox 360 Average Sales Per Year: 8.77m