As said in a sibling comment, Windows Internals is a must-read. However, you are correct -- NT4, 2000, and XP saw the addition of lots of stuff inside of ring0. However, most of that was independent of the actual NT kernel, and since Vista the trend has been reversing in a huge way. There's more in ring0 than there was back in the day, but a lot of stuff has been moved out, e.g. many drivers, even video drivers. The new (relatively speaking) usermode driver framework makes it trivial to write drivers that don't run in ring0, and the kernel now has fewer dependencies than ever.
NT has had some growing pains architecturally speaking, but it's been handled remarkably well. Probably the best thing to ever come out of MS, especially when you contrast it to the mess that is the Win32 subsystem.