Windows 2000 is my all-time favorite Windows OS. NT-based kernel, literally nothing extra, fast, stable. Used it til the day support was finally shuttered.
NT might be more stable but it was also much slower. DOS applications on 9x actually ran in a VM with hardware passthrough, whereas NT emulated much of the hardware via NTVDM. Interacting with something as simple as the EDIT text editor in a window on 2K/XP is noticeably slower than on 9x.
I think you're mixing up Windows 2000 and ME? ME was a rushed update of 98 because Microsoft felt "they should release something" for the Millennium. It was a dumpster fire. Windows 2000 was the continuation of Windows NT, and became the basis for XP and everything that followed.
As for performance, by the time Windows 2000 came out (Pentium 3 era machines) it didn't seem to matter that much any more, and it really was a lot more stable.