I couldn't even force myself to finish the first game, so I'm not going to bother with this one. I finished about 75% of the first but that's something for another thread.
My first reaction when I read that you could play as a big daddy was: Why would you ever play as a big daddy? They're limited to either a melee attack or some nail gun and the ability to throw things.(I think it was a nail gun, can't remember) Sure, even with the limited possibilities of that you could add fixed areas to change your weapon.
When I saw that you get magic... Why? What's the point of it? Yeah, you're some special big daddy, isn't that great. Why can't later big daddy models use magic? It would certainly help it's ability to protect the little sisters.
Hell, it would have made more sense if they made the big daddy you play as some form of experimental one. One designed to replace the little sisters. Strong ADAM collector with some minor magic abilities to protect itself. Being an experiment, it would make sense that you don't exactly behave like a regular big daddy.
I would type more, but I'm tired so I hope this explained what I was trying to say.