Riot’s focus is on refining existing experience so the time you spend playing League is as satisfying as possible. They’ve got four major themes this year:
laning phase is improved and slightly longer;
comebacks are more achievable and satisfying;
decided games resolve faster;
rune paths no longer dictate stat bonuses.
As is customary, there are also bunch of changes that don't fit into those buckets too (Lissandra has a real passive now!).
This is the first sizable patch in a few months, so watch quick view of it and read more specific info by clicking this link.