vista's aero was like a half-baked cookie, it wasn't delicious at all.
i don't know if you can disable aero in vista but in win7 it can, also win7 when stripped of it's features is lighter and a tad more responsive than xp.
Aero is pretty much the same in both Vista and 7 in terms of functionality (and yes, it can be disabled in both). The main difference is that they optimised it quite significantly in Windows 7, so it's no longer such a resource hog (although it was hardly the most resource-intensive part of Vista, either).
As far as too aggressive is concerned, couldn't the same argument have been used going from 3.11 to 95? People are going to cling desperately to whatever old system they're used to no matter how slow you go, but sometimes you need to shake things up rather than introduce new features at a glacial pace. I dunno if Metro is it, but it was a pretty big leap going from program groups to a start menu.
if i remember correctly 3.11 was purely DOS right? 95 still has a DOS emulator which kind of amended the hate from the transition. the thing that made windows8's UI hate-able
Windows 95's big change wasn't related to DOS - you could still run DOS programs from Windows 95 just as easily as from 3.1, and it still came with DOS installed, so you could easily switch to the full DOS OS if you wanted to. The big change in Windows 95 was adding the start menu. It was very different to the old system of program groups, which is why some people were concerned when it was announced, but IIRC once it was released, most criticism dried up right away because it was such a big improvement. Unlike the new Windows 8 interface, which is considered by many to not be better; hence the ongoing criticism post-release.