If majority of the leaves have dried it is invalid.
The definition: The definition of dry is if the leaves have dried to the extent they lost their coloring and have turned white. If they have not yet turned white they are valid even if they are dried to the point they are withered [and can be broken with one’s finger nail].
If the leaves droop downwards:
If majority of the leaves have become detached from their original place of growth and hence droop down, they are invalid, even though they still remain slightly attached to the actual stem.
What is the law if the leaves droop downwards but are fully attached to the stem?
Some Poskim question its validity. [Although it is implied from Admur that they remain valid.]
 The reason: As it is no longer considered Hadar. [ibid]
 So rules Admur ibid.
Other Opinions: In the SHU”A of Michaber/Rama it is not stated what level of dryness makes the Aravos invalid. Thus some Poskim are stringent if the leaves can be broken with the nail even if they have not turned white. [Sefer Arba Minim by Rav Shtern]
 Piskeiy Teshuvos 647/3; Kashrus Daled Minim p. 141