windows was originally a better GUI for DOS than the one they had already. remember that MSDOS was a hack of QDOS which was a hack of CP/M. MS never actually ever properly mastered MSDOS, which is pretty poor since most of their products were based over it for about 15 years.
Now as for windows, after about windows 95, it starts to get funny. it's still a GUI for DOS but now it has a lot of shit like extended memory and a whole slew of other stuff that DOS just cannot do on its own. A lot of dirty hacks need to be run to allow windows to make a fair attempt at behaving like an operating system even though it has MSDOS hiding underneath right up to 2000 (as Bill Gates once said about MSDOS "640k ought to be enough memory for anyone").
But back to 1995 for now, windows NT is coming along fairly fast. It's an operating system built primarily because too many people know or are figuring out how DOS (and by extension windows) works. Not good if you want to have your monopoly and eat it too, so they take 5 years, phase out DOS completely and steal what they can (BSD TCP/IP stack, anyone?) and kludge together the rest into what amounts to a complete clone of window-on-dos as far as GUI goes, but under the hood you have three new approaches:
1) make it as arcane as possible so people who figured out DOS are still kept guessing for years. I bet MS are patting themselves on the back for NTFS, how long will it be before somebody figures out how to implement that in a real system? and in the meantime hordes of clueless newbies (and morons too) are being conned into converting their drives to the useless dead end NTFS filesystem.
2) for gods' sake make it look as though all your old win32 programs will still run on it. It doesn't matter if they really do run, people tend to be satisfied if their old programs kind of work, and their old games might die after the intro screens, but that's okay. They'll upgrade their programs and buy new games. Let's face it if their old programs did not even
look like they might work, those people might never buy the system in the first place. As it is, they think that program works with everybody else's machine (because they saw the startup screen) and there's just something wrong with their personal machine/windows combination.
3) spyware! microsoft realised recently that what with it losing money hand over fist fighting court cases, allowing flagship products to go out as loss leaders and using pirated software as a form of advertising, it would need to find a new source of revenue. Market research is it. Hundreds of companies will pay through the nose to get real statistics about your every little twitch and whim on your computer, and if you use microsoft windows XP or any later microsoft operating system, you will (i have heard) be obliging them by allowing them to collect any data they wish, and alter the contents of your hard drive if they feel like it.
see here for more details.
So you see microsoft windows operates in exactly the way it is intended to run. To me using linux at home is like being able to explore a huge fully furnished castle, and using windows afterwards is like arriving at the castle, and entering to find it is a completely hollow facade, without even floors or walls.