Change is only good when its an improvement.
Now to each his own, but my opinion has always been that the best tool is the one that lets you do the job in the least amount of time. For me, that's the Windows 7 Start menu. Most of what I need is never more than 2 clicks away, and even if I have to open a program I haven't used in a long time, it's fairly easy to find the program. Everything is contained in a nice, one-dimensional list that's easy to parse.
The issues people have with the Windows 8 Start Screen is that is is not an improvement for people that have a large number of programs. The first problem is that the Win8 Start Screen is two-dimensional and very cluttered. It also does not allow for nesting of folders, making it harder to find an entry.
I've done a lot of work with UI's, and the one thing I have most consistently discovered to be true is that our eyes do NOT track well in two dimensions: we find things better when we can move along a list in a straight line, not when we have to go up and down and left and right. (This is my chief problem with the Office Ribbon, too, btw.)
The other problem is that when you're using a large monitor, assets designed for an 11" screen just look ugly and take up a lot of space. I bought a large display to have more room to display text and images - not to have those things blown up to 2 or 3x their proper size.
And to make matters worse, WIndows 8 is not even a good tablet OS. I've already sold my Win8 tablet because it was just slower and more awkward to use than my iPad or Nexus 7.
And there's the legitimate complaint of people having to re-learn how to do things. Your time is an investment, and it's not fair to ask people to throw away that investment and start over when learning how to navigate an OS. That is a perfectly legitimate concern, and everyone who discounts that issue is being both short sighted and not looking at the bigger picture.
While I appreciate the under the hood improvements in Win8, I don't think Microsoft has really succeeded in creating the iPad killer they hoped for. Instead, they just managed to take Windows 7, the best OS they ever delivered, and cripple it with a UI that makes things harder to do.