After many complaints for years for the Adobe AIR client, Riot has revamped it and the changes are already visible on PBE.
The new client will not only be less of a resource hog and more optimized, it'll also show a lot more relevant information in the user interface. Information such as the "Free champion rotation" with champion stats and relevant news directly above it take precedence over filler material.
For the first iterations, Riot has stated that they "aren't going to redefine your pre-game experience" as currently the old rune and mastery page systems are in place, but it's a start to a brighter future. Riot will be switching from Adobe Air to a much more modern approach with HTML 5.
Source - Riot Games