Win7 is basically Vista 2.0 -- Vista was terrible and I mean terrible but Win7 was much better. So, to answer your question: Vista =BAD while Win7 = good. Win10 is about ready to come out and many are using the beta versions but there were beta users of Vista as well. We won't really know how good or bad Win10 is until millions of people have it.
I have not clicked on "reserve" for Win10 so I don't know with certainty what reserving actually means. It could be as some indicate that it just notifies you when it's available OR it could mean, as other indicate, that when it's ready it will automatically update. So, if it's the latter then this will tend to get more people to jump onboard earlier AND before they know if it's Win7 good or Vista bad.
Brian
I used Vista from day one without major issues(over two years including beta games testing for companies),Vista had too much UAC nagging and some file transfers was a bit slow ,only things I remember back then,but it was very stable for me,a lot of companies were very lazy getting Vista drivers out the door(remember could not use XP drivers unlike Win7 which had Vista drivers in general to fall back on),also OEM shipping hardware below Vista's minimum recommended specs did not help,throw in FUD and damage was done.
End of the day every OS gets improvements/fixes with time regardless of Windows or Linux,OS in question will always be a preference thing,good and bad is relative to the user in question,take you and I for example ,we already have different viewpoints on Vista and we both have personal experience with Vista.
As to Win10, a lot of users have tried the many builds out there,Microsoft are putting a lot of time and effort into it,game companies will jump on DX12 side.
Again the Vista bad and Win7 good is a very bad anology,I know some people that refuse to go to Win7 from XP, does that make Win7 bad?...Again it's only your view point.
Getting back to Win10 and forgetting about old OS like Win7(remember only five years left to EOL for 7),I think 10 will succeed,I'm not naive to think there won't be no bugs or issues, but then I could say same to you about Win7 on its initial release and that had Vista has a template/guide to work with but still had bugs etc..
Regardless I'll be jumping to Win10 because I like what I have seen and used,and this from a person that has had a very stable Vista,Win7,Win8/8.1,yes me ,what the heck throw my Linux distros in as well(stable too).
We can also thank Vista for pushing 64 bit OS and drivers out the door,yes I know XP had 64 bit OS but it was only from Vista that really pushed the way forward for 64 bit drivers and OS due to Microsoft's policy with Vista and OEMs.