Linus mentions in the 4.5-rc2 announcement that he was happy with how this release was turning out, but since Friday there were many more pull request submitted. The amount of new activity in the past few days though doesn't worry Torvalds and is the result in finding bugs by users/developers in trying out Linux 4.5.
The Linux 4.5-rc2 changes are scattered throughout the kernel's many subsystems. If you aren't familiar with the many new features of Linux 4.5, see this Linux 4.5 feature overview. Linux 4.5 will likely be officially released in six to seven weeks.