I am generally pleased with Windows 7. It seems to perform well and is generally usable but there are some things that are annoying about it. At the end of the day, an operating system is just a platform to run productivity applications, it should not be any real beast in its own right and should not get in the way.
My biggest complaints are changes. For instance, trying to get into the various options screens of Windows Explorer is horrifically complicated when you are used to the older way of Tools-Options, a fairly universal concept that millions of people were used to. Now they are spread across various unintuitive icons and menus which look like they were 'designed' by a child.
Another thing which I come across a lot is the renaming of standard shortcuts so you can't find them. Most of us were used "Add or Remove Programs" which has now been renamed to "Programs and Features" which doesn't really say much differently except it is now in a different place in the control panel because it starts with P instead of A. Why are people allowed to change these? If you want to mention features, call it "Add or Remove Programs/Feature". When you test these things, you would think somebody would notice and complain.