For describing all the implementation details of most intel processors, I'd kind of expect it to be that size. In any case, while it might be huge, if you have a look, a lot
of the manual is for advanced features that won't be used for quite a while, so there's no need to feel super daunted.
Most of what you need from the manual is described in chapters 1-8 (and maybe chapters 9 and 10 if you're using multiprocessors). That only makes up about 450 pages max, so if you've got some time, maybe have a read through some sections which take your interest (Chapter 2 is really good, it provides a good overview of how the entire processor works and the important features). Even just skimming through the manual will give you an idea of how detailed and useful the manual is. If you end up just using chapters 1 - 10 often, you can get just the first section of volume 3 from here (Volume 3A)
It looks scary at first, but the more you read it, the more you'll realise it's just very, very, very