Indeed the framerate is low, the movement choppy, and the camera always leaving too much space over the minifig's head.
But, I agree with Nate, you are braver than us in deciding to adapt a musical number in this medium (especially one as gorgeous as Good Morning), and the mouth movement is quite accurate. Also, I really like Singing in the Rain.
A few things that may help you in future:
It's not interesting to see large portions of the frame where nothing happens (like lot of space above the heads, unless it's on purpose, but then again, if it's on purpose, something is happening), and in here it caused that sometimes you left out parts where we were supposed to see things going on: there are some parts where you can't see the feets of the minifigures, and since they're dancing, you might want us to see it. Try to frame your objects appropriately, because, being a movie, it's important to decide what you're going to show. Also, be careful with lighting, use more than one source to light sets and characters properly, without making them appear flat.
About the framerate, increasing the speed is not enough, I've seen great animation at 10 fps and awful animation at 24 fps: what you should strive for is to get the movement right at the framerate you feel more comfortable working with.
That's all. Also, thanks for adapting that scene: it's been some time since I last saw the movie, I always enjoyed that part especially, it feels good to see it again.