If there was an Award for the best looking OS, Vista would certainly be in the running. Even I must admit the Aero Interface looks pretty cool, with those nice transparency effects and I feel Overall Vista feels more smart compared to XP. Unfortunately looks take a back seat to usability and that's where I feel vista is a disappointment for me.
One of it's flaws is it's need to be a resource hog, Even in basic mode (Aero turned off) Vista eats system resources. Does Microsoft really think this bloat is necessary? Yeah sure Vista is going to demand more than XP (logical), but I don't bide all this nonsense 'The reason why it is bloated is because it's for future hardware'. Even Simple tasks in vista feel slow like copying files or opening menus . Look at some of the Linux Distributions, like the excellent Ubuntu, which feels light while offering some nice improvements with each edition. Linux will never compete with Microsoft in the mainstream, but for the mainstream user, the older XP is still a sound choice and the everyday tasks will be quicker. Hardware wise XP will also use Dual, Quad Core etc, so it's not even close to being obsolete.
Another claim is Vista's more secure, I do agree Microsoft has done ok. By Default Vista has some nice security tools included like Defender, parental controls and User Account control. Even though I do agree that such features are welcome especially for the novice computer users, XP can be made just as secure with some simple downloads and Vista will still need a third Party Anti-virus solution. If you want a truly secure operating system use Linux
Gaming wise Vista Includes Direct X 10, but from my experience, it's to early to be an essential feature for a gamer. The DX10 games I have managed to play was kind of a 'spot the difference' affair between the DX9 mode while suffering a performance hit. Bioshock actually looks worse because AA cannot be enabled while in DX10 mode. Lets be clear I am not blaming Microsoft for this, because it's up to the developers to make the best use of the new features. However buying Vista for the DX10 hype is really not worthwhile from my perspective, well at least not yet.
Compatibility is another issue, there is some software and games that just will not run on Vista. I have experienced a variety of software titles that either did'nt work or crashed randomly. If the software developer does not issue a patch or there is no known workaround fix, that software title becomes pretty much useless. Although to be fair if a software title was designed for XP, then there's no guarantee it will run on Vista. I can understand that, but I believe Vista has caused me more compatibility problems with existing software, than my past experiences with previous Windows Editions. I believe Microsoft could of Improved compatibility, even though reasonably it could never be perfect.
In time Vista will be on most computers, but only because Vista will be the only choice for new computers/computer builds. In time Vista may get better with service packs, so watch this space.
I really like Linux, but I very much doubt it could become a mainstream choice like Windows.