Once you do learn enough Linux, and have an SD Card to spare, it can be a fun exercise in learning to build your own Linux + clib + GNU Tools + X11 + WM + Desktop Environment + all the programs you want. Once you have done it completely from the ground up, starting from source, you get a better appreciation for what the system is, and a little better understanding of the standard way in which it is done.
It would be nice to have a few things different for reasons of performance, such as a purely local API GUI, that uses direct dynamic linking for its interface instead of X which communicates with the applications over a socket protocol, would also be nice to have a better thought out process tree than spawning off of init.
Though Linux follows a model that is derived from that of many other *n*x systems that came before. Linux is just the first to diverge from the others far enough to raise questions of weather it can really be considered a *n*x at all, or if it is a different class of OS with some similarities to Unix (Unics, Castrated Multics
It can also be interesting to play around with some other OS's from history, like RT/11.
Linux is a usable OS because of its wide support. Linux is an attempt to preserve a dead line of OS's (very successfully [Linux is the most popular OS on earth today]). I use Linux just because of the supported software that is not available outside of Linux on NON-Intel based systems (like the ARM based RPi). Though realistically it is still a Unix like OS, and as such it still has the usefulness of traditional Unix. Traditional Unix is great for systems that host a great number of terminals, as was needed in the days before people could afford personal computers. Timesharing systems were falling behind, multitasking multiuser OS's were the solution for the big computer installations, a thing of the past.
Even X was designed with this concept of terminals in mind, hence a protocol for remote display of graphical applications (which is what X is), using a socket interface.
Now it would be possible to build a decent OS on top of the Linux Kernel, an OS that is NOT in any way Unix like. Though I do not foresee this happening in a usable manner in the foreseeable future.