The kernel is simple and sanely designed and interfacing with it is done through the filesystem in, again, a very simple and sane way. Your displays are configured by a simple <10 line shell script at boot time that writes plaintext to a device file, rather than a gargantuan graphics stack that's controlled with binary device files and ioctls. Filesystem namespaces are lovely, and make the filesystem cleanly organized and customized to the logged in user's needs and desires. I have a little script that clears my current terminal window: `echo -n "" > /dev/text`. The libc is small and focused (non-POSIX), and there are only a handful of syscalls. The process model is really sane and straightforward as well. Playing an mp3 file is `mp3dec < file.mp3 > /dev/audio`.
To open a TCP connection, you use the dial(3) function, which basically does the following: write "tcp!name!port" to /net/cs and read out "1.2.3.4!80" (/net/cs resolves the name), then you write "connect 1.2.3.4" to /net/tcp/clone and read out a connection ID, and open /net/tcp/:id/data which is now a full-duplex TCP stream.
There's this emphasis on simple, sane ways of fulfilling tasks on plan9 that permeates the whole system. It's beautiful.