There is a great view from the hallway window that is closest to the elevator in the North wing. Just take the elevator that is closest to Roaring Forks up to the fourth floor or higher and go down the hall toward the left as you get off the elevator. These windows are very close to the elevator. You'll have to open the window shutters to get the good view, but don't worry, they won't say a word about it.

You can even see the low fireworks from these windows. Rule of thumb is if you can see the castle then you can see the fireworks.
We watched the fireworks from Geyser Point in March and it wasn't too buggy. The nice thing is that they pipe in the music at Geyser Point. But the view isn't as good as from the north wing hallway window.