I've been riding the Windows train since 3.11, and I've gotta say 7 is all right.
95 was such a huge leap from 3.1, but 98 and 98SE ...eh, not so much.
I administered and supported NT4 in an enterprise environment. I had a love-hate relationship with it. There were things that I wished I could do with NT on my '95/'98 boxen at home, and vice-versa.
Win2000 floored me: I loved it. Multimedia + ease of use + NT and all that came with it? Sign me up! Loved it.
I stayed away from XP until early 2003 or thereabouts, but fell in deep like with it. Sure, in a lot of ways it was just a reskinned Win2000, but in a lot of ways it was better/different.
Windows Vista - I think MS is at fault on this one (obviously) for understating system requirements and an over-reaction to XP security vulnerabilities that could be accidentally opened by users, but some of the blame lies on OEMs for poor driver development and crapware pre-loads.
I ran Win7 on a VM on XP. On that VM, I had allocated half my RAM (1gb), and it typically used about half my CPU power at the time (1.1ghz) and aside from no Aero support (I think it was actually VirtualPC from MS I ran it on and the minimal video card emulation in there can in no way support Aero), it was fine. I didn't have nearly as many nags with the UAC, I ran Office 2007 (EE), installed Firefox 3, surfed the web, used it for general tasks most of the time. It wasn't like oiled glass or anything but it still worked and worked well, and for a beta, was entirely stable.
When the final release hit I picked up a student discounted copy, and have been using it since. Good OS.