For many, it might be too much. For me, and possibly others, it was exactly what was needed. I wanted to learn about things like partitioning (I had just destroyed my family's HDD while using another distro's GUI installer, and wanted to know how do it the right way). I tend to be a bottom-up learner. Years later, when I started studying computer science at a university, I would be more interested in assembly than java. The approach has served me well, but others certainly benefit from learning in other ways.
It's the deep end, but there's VERY detailed and explicit instructions on how to swim. And almost zero risk of actual death.
I wouldn't recommend it for someone who's never touched *nix before, but if you've installed Linux, and run apt-get a couple times, it's enormously edifying.
I never felt like I "got" Linux until I installed Gentoo.
Most of the things you'll "learn" with Gentoo are how to get such-and-such a package to agree to build & install. Gentoo is all about groveling through configs because you're stuck in a 1993 mentality of trying to save 100 kB in your binary by excluding GIF support in Firefox and stripping symbols out of /bin/ls.