The old client's tech has been fully replaced with a new, more reliable foundation so we can fix long-standing bugs and set the stage for League's evolving future. We also took the opportunity to rework the client's visuals with a cohesive (and kinda sexy) hextech design.
Although updating the client was mostly about preparing for the future, we couldn't help but build in a few exclusive new features for those who upgrade. Drag and drop rune pages to reorder them, or see in-game ability scaling information and change your in-game settings—all from the client. Oh, and all future features (Replays and Practice Tool!) will be exclusive to the updated client.