It absolutely was an important (and required) step towards a more secure and stable OS. What it was not, though, was a secure and stable OS.
Windows ME was the same. A required step on the path towards something better, and ALSO something that had the "Windows XX-ready" badge slapped on anything that asked. But no one is lining up to try Vista again apart from technical challenges.
The list of changes Vista made were never going to go off without a hitch. When you put new boundaries in place in the kernel, and a driver violates them because it was recompiled not updated to handle a separation and handle errors from it: there's no choice but to Kernel Panic.
Compatibility Shims were introduced for userland changes.
Despite the hate, DWM handled the most frequent crashes: graphics.
Microsoft is STILL working on pulling graphics code out of the kernel and into userland.
Every Windows version was a "step towards a more secure and stable OS". The issue is: they never get there.