Vista brought a lot of good features and improvements, but it required very high specced systems and ran like garbage on the lower-end systems that were common at the time. It tried to make too many changes too quickly.

It also had a bunch of driver issues, because it introduced new driver models that were more reliable/stable, some of which are still used today, like WDDM (Windows Display Driver Model) for display drivers. This required manufacturers to make some big changes to their drivers, and not all manufacturers are great at writing drivers.

So yeah it was kinda terrible at the time, but it laid a mostly solid foundation to build on top of. By the time Windows 7 came out, PCs had better specs, and manufacturers had fixed all the issues with their new drivers. Windows 7 was good because of Vista, not in spite of it.