Why is the word "Probability" a link to some weird studying website? possible spam weirdness?
I'm not sure I'd call Windows "Brilliant" in the sense that it is markedly more technically proficient in construction than it's competitors; OS X, Linux, Unix, and Windows are all complicated because of their construction over time and they all include intelligent programming, but perhaps some of the "Brilliance" attributed is largely a result of not understanding it. Like the old saying that any sufficiently advanced technology can be effectively magic, any sufficiently complicated software system can look brilliant.
I think a better angle to consider whether a piece of software is "brilliant" is that it breaks new ground and really pushes limits to provide unexpected features. I don't think Windows necessarily qualifies here.
One thing I think does qualify is 4K Altair BASIC. A Full BASIC Interpreter that included a line editor, custom input/output handling, not to mention a FULL software emulation for floating point math- all fitting within 4K of RAM.
This web page is several times larger, just in text, than that entire program. Not to mention that when going to demo the product, it was suddenly realized that they did not have a Boot loader- and they wrote it on the plane on their way there- no IDE or development tools or even hardware access at all. THAT is brilliant.
Another example might be something like the Quickdraw routines used in earlier Macintosh systems.
