As late as Friday, I was planning on talking about how nice it is to see this new trend of tiny rc2 releases, because there really hadn't been very many pull requests at all.
But it turns out the pull requests were just heavily skewed to the end of the week, and 4.5-rc2 isn't particularly small after all. It pretty much doubled over the weekend.
Not that it's all that big anyway, and skewing towards the end of the week probably makes sense for rc2 - it takes some time to start finding the problems that the merge window has brought with it. So this odd behavior doesn't worry me, it seems fairly natural.
As to the kinds of patches we have here: the appended shortlog gives more details, but it's pretty much all over. Drivers and architecture updates are only about half of the patch, with perf fixes and some of the new virtio self-tests being much of the rest. There's some btrfs fixes too.