The best way to describe Vista is "hit-or-miss."
For 64-bit support, Vista is the way to go, as XP x64 had little to no driver support until Vista came along.
Vista RTM had A LOT of problems: trivial apps like the sidebar using up tons of memory, file copying taking significantly longer than XP, Windows Update failures, some networking issues. Other problems are more the issue with manufacturers for not writing drivers for Vista and developers of legacy apps for poor development practices (i.e.: coding their app to assume administrative rights for everything).
I NEVER recommend using Vista RTM on any machine with less than 2 GB of RAM.
Vista SP1 created a near 180 degree turn for the OS: file copies were fixed, networking was fixed, bloated items were optimized a bit--the OS can actually run with 1.5 GB of RAM (and even 1 GB of RAM after SP2!!!)
Between stupidly lower RAM prices, Vista SP1 fixes, and developers and tweakers alike finally wising up to Vista practices, Vista starting becoming a decent OS. However, the damage to Vista's reputation was done:
1) XP was "good enough." Vista was just change for the sake of change. At least XP provided obvious benefits to home users that were using 98 and Me. 2000 users didn't warm up as fast, but XP was at least similar enough to 2000 to not cause too much discomfort...
2) The Internet age allows (mis)information to spread faster than ever before, which is why Vista gets slammed harder than XP did when it first came out.
3) Microsoft "forcing" Vista didn't help much, either. DX10 could probably be backported to XP if Microsoft wanted to do so. Halo 2 and Shadowrun were DX9 titles, but they were artificially locked out of running on XP.
4) Basic tasks all of a sudden became more difficult to do. Want to boot more than one OS? You have to edit BCD. No more boot.ini.
5) User Account Control drove people nuts. Granted it was a very sound idea: run Administrators as standard users, and elevate only when the user grants consent. However, people want instant gratification (even if it does bring about drastic consequences).
6) Tools that were originally in XP are no longer in Vista. Examples are NetMeeting and HyperTerminal.
7) Microsoft and Intel mismanaging the "Vista Compatible" program didn't help matters much...
Too many options can be just as bad as too few options at times. It's even more confusing in the case of Vista Home Premium versus Vista Business when it comes to Media Center: Vista Business is more expensive, but doesn't even come with Media Center, wheras Vista Home Premium comes with Media Center...
9) Finally, needing large amounts of RAM just to run an OS seemed absurd at the time...
Despite all these gripes, in my humble opinion, I do think Vista is now a good OS. Even if it's burned at the stake and will only be remembered as the Windows Me of the late 00s decade, it IS the building block of the not-yet-released-but-heavily-praised Windows 7 (as well as both Windows Server 2008 and Windows Server 2008 R2).