This is the first tagged development release for the Linux 3.11 kernel after its merge window was open the past two weeks. In this time, a lot of features were merged although Linus says it wasn't as much as Linux 3.10.
For details as to the features of the Linux 3.11 kernel, read The New & Best Features Of The Linux 3.11 Kernel. Most notably is the Radeon dynamic power management support, Radeon HD 8000 series GPU support, stabilizing of Intel Bay Trail, Nouveau VP2 video decoding support, Lustre file-system support, Zswap, ARM improvements, and much more.
While the release announcement is quite brief and doesn't dive into the major features of 3.11-rc1, it can be found on the kernel mailing list archives. Now with -rc1 being tagged, you can expect performance benchmarks soon on Phoronix of Linux 3.11!