I would have to disagree, sir. Vista had a bad launch, but it's very solid. It's basically the same as Windows 7 under the hood. I never had a problem with it, even when I made it do things that it wasn't made to do.
For mainstream OS's, I would give that honor to Windows ME.
Mainstream OS's? I can't think of a non mainstream OS that was worse - unless we're going back to the days of QDOS (quick and dirty operating system.) That was dreadful, but at least it died a quick death back in the 80's.
Oh wait... it didn't. Gates bought it and turned it into windows
Hated the Vista all through out it first creation, maybe the design phys-ch me up... loved the XP series and tried the & series! It almost like XP new cooler Brother. Both Xp or 7 i opt out for 64 bit config.