I don't understand what's "so pretty" about it. Other than the fact that the manga says it's the most beautiful sword it's merely just a white blade, hilt, scabbard, etc. So from appearances it's nothing too special.
And, I agree. Her shikai already has three special moves. First one kills an arrancar. Second stops an Espada in his tracks. Third kills an Espada. Wth? Where'd this power come from? I remember back in issue 1 a very weak Rukia getting pwned by a mere low-rank hollow. Thus the whole reason for transfering her powers to Ichigo and starting the series.
If she had a zanpakutou that was capable of such damage (she could probably kill a captain with it given he doesn't move out of the way), you'd think a low-level hollow would be a piece of cake for her. It just breaks continuity to have her reveal her zanpakutou to be something so uber.
Would have been better to have been revealed as a zanpakutou not unlike some of the others seen and just have her improve with training from Byakuya or something. I mean, three special moves? For all we know, she has a fourth dance.. fifth dance... etc. Everyone else barely gets ONE specialty. Some don't even manage that. Ikkaku, for example. The main character of the series has but one move. Getsuga Tenshou.
Rukia's zanpakutou is cool and all... but it's power is a bit much. I call shinanigans.