I love DDR and it can definately be a hard workout!!
It is also really hard and I got discouraged really fast until I discovered workout mode... you can easily adjust the difficulty level for this.
As far as being a good dancer, you do not need to be.. I think you'd look rather strange doing DDR dance moves at a club or something (then again DDR is pretty big now.. so maybe it's cool now lol)
It takes coordination more then anything... FI and I also picked out these mats with sticks that you can play fighting games with... basically these sticks have sensors to detect when you kick and stuff... great workout.. but they take so much room in the living room