This is about as complicated and legalistic as it gets. But it’s a rather startling decision.
The Senate has increased its use of the filibuster (which ordinarily is not technically a filibuster any more; see this) in order to block appointments. And so presidents have increasingly made recess appointments in order to work around that, and it’s reached even greater proportions with Obama. This ruling would make it harder to do so.
But whether it will ultimately be upheld is anybody’s guess. For an interesting back-and-forth discussion, please read the comments at the linked post, too.