Why does everyone say Vista is bad?

You mean, aside from the obvious? Look at Vista; what do you really get? A spiffy interface, some add-ons, a new tool or another that serves no practical use, some modifications that complicate life more than help, support for a new DirectX version that's meant to help only people with good VGA cards, since the better 3D effects require a GPU to go with it, it's an incredible resource hog.... See where I'm going here? There aren't really any positive features to Vista despite what some people may say. Sure, probably they didn't got a too bad experience out of it, but it was such an unoptimized system that it just couldn't work and that's why we got W7 today. Looking at it from an angle, Vista kind of feels like a Beta of W7's own Beta and RCs, but Microsoft spewed it out anyway as a whole new OS and tried to suck people in. Kind of worked... Most people though were unhappy with the new OS, specially due to the resource requirements. Brand new computers were being sold with Vista as its bundled OS, even if the computers could barely run Vista and still have resources for other things, which of course left people unhappy especially as Microsoft tried to cut off everyone from XP and drive them to the crappy new OS; themselves aware that W7 would be vastly superior and if people were in Vista they'd feel almost forced to upgrade to the new operating system. So, in short, there was nothing good about Vista. XP had efficiency even if not all those little gimmicks. W7 shows that it's possible to have near XP's efficiency and still throw in those gadgets and stuff; so clearly Vista is a flawed product.

The most important reason is that vista is much slower worse compatible than xp. In other ways, vista does well than any version of os before.

I think it is because it was just so different and didn't go along with many other programs, I refused to put Vista on my computer and I am so glad because now I have Windows 7 and I am very happy with it...

It's just because vista is not that good as windows 7. Too many negative feedbacks. I still use windows xp rather than vista. Someday, people will realize that they need to be aware of windows vista or windows 7. Technology is growing too fast.