The Starfall buff looks to be exactly that, an excellent buff. But remember, this is PTR patch notes, and they are certainly subject to change before the patch goes live.
However, IF this goes live, the Starfall buff will be an extremely nice one for raiding moonkin, and you’ll probably end up switching out your IS Glyph for Starfall before it’s over if Graylo’s math is right.
There’s already lots of information floating around, so instead of rehashing, I’m going to direct you to the places I think do the best job of explaining the changes:
For a strictly PvE understanding with accompanying math, check out Graylo’s post about it: “Starfall Buffed.”
For an overview of the changes, especially for you PvPers wondering what this is going to affect, see WoW.com’s “Starfall and Nature’s Grasp PTR Changes.”