Aside from the obvious- (the half zip feels more like a pullover and the full zip has more of a cardigan feel)...
The full zip has the useful little zip pocket in front to keep key or $20 in. I find it very handy for my locker key, a chap stick, and a couple of dollars when I'm roller skating at the rink. Also sometimes if it's below freezing outside I will slip my cell phone in it to keep it from freezing during my long walks. It's just big enough for a cell phone and some folded $, etc.
The material is the same, neck is the same, sleeve length, seams, same.