Utilt is quite good. It has the vertical hitbox of the usmash, if not just a tad more. It can double hit when it is optimal respectively to range and DI, doesn't decent damage, comes out rather quickly, and sends opponents away far enough so that you can't really be punished unless they shield and OoS. Unfortunately, it's also rather easy to punish at the same time because the intervals between the first and second hit is rather long for a single move, and can easily be perfect shielded to OoS. It's not the best option to go though since rarely you find yourself in a situation to use it when you can risk for a tipper Usmash or grab from a Ftilt lock.
In comparison to other characters, Sheik's Utilt is good, unfortunately, so is everyone else's. It doesn't have the range of Marth's utilt, the crazy power like Zelda's, nor does it have the crazy disjointed hitbox like Peach or Snake's. However, it still is useful when the situation calls for it, and if you need to refresh some of your more used moves.
6.8/10
@ Blistering: I don't know, I like attaching a number to moves since I tend to compare a move with other characters instead of Sheik's moveset. It gives me a sense when comparing one Utilt to another.