When Windows ME was released, it was little more than a reskin of Windows 98 that removed or disabled much of the 16 bit capabilities and support for the ISA architecture in favor of 32 bit and PCI. It couldn't be installed on most existing machines and was highly unstable on those that it would run on.
Windows Vista wasn't much different. It was a crappy skin and a new desktop composition paradigm requiring better underlying graphics hardware than Intel was providing at the time. Many systems couldn't upgrade to it and those that did had stability issues due to immature graphics drivers.
Windows 8 was similar, it introduced a newer kernel design that fully extracted Win32 out to userland. It also introduced Metro and other modern elements that weren't bound to IA32/IA64. It was primarily targeted at modern single screen touch enabled devices and didn't work well as an upgrade or on desktop PCs. They eventually shipped Windows 8.1 which was largely a refinement of 8 that was arguably the test bed for extending Windows 8 concepts to the desktop.
Very little of this is true. Windows ME runs all the 16-bit code you can throw at it and supports all ISA devices identically to 95 and 98. Windows 9x were just as 32-bit as ME and supported PCI just fine.
The only thing they removed support for was booting into real-mode DOS, and started ignoring your autoexec.bat and config.sys files for the most part. You can hack that back into the OS pretty trivially, it's purely cosmetic and has nothing to do with the underlying architecture. They probably did this in an attempt to hide its creaky MS-DOS roots, and to get customers more used to not being able to run pure DOS before the inevitable shift to NT.
Windows ME was a product even Microsoft seemingly didn't really want to make -- nothing but a last-minute stopgap measure until they got XP ready. No one liked it at the time as it was basically Windows 98 but worse. There are some good parts, though -- improved USB support, for instance -- and therefore there are now projects that "backport" features from Windows ME to Windows 98 so you can get the best of both worlds.