> IME Unity makes it very easy to do the common tasks of opening a specific app whether or not it's running (just click the launcher icon) and opening a new instance of an app (middle click instead).
Middle click is extraneous to most people, and it's unnecessarily difficult on a laptop. I would not argue that Unity makes it easy.
> This is as opposed to old Gnome 2 and other desktops where you have at least two different places to go (task bar or menu/shortcut) depending on what you want and whether the app is already open.
People are used to this. It's how most computer UIs work. It's what everybody that has used a computer has come to expect. Unity feels awkward just for the sake of being different. It's not difficult to guess why many people don't like it.
> Works very well after you get used to it. Especially if the number of frequently used programs is small enough to comfortably fit the launcher.
Too many requirements. What about those that do not want or do not have the patience to "get used to it"? What if your list of frequently used programs is big, or changes frequently?
To be frank, the only people that I can think of that benefit from Unity's design is people like my mother-in-law. She used to let 7 o 8 Firefox windows open in the old Ubuntu Netbook Remix until I came to close them. For some reason, whenever she wanted to look up something with Google, she just opened a new one. Now she can reuse the old instance (but adds a new tab, she cannot be bothered to click on the home button to reuse the one already open).