I believe you can turn off unified menu (by uninstalling the packages) independently of switching window/session management from Unity. At least, that was the case in 11.10.
Unity has other quirks that make it irksome to me though. For example, the single icon for all windows of the same app makes it very difficult when working with sets of similar-looking windows - terminal emulators, for example. Also having no option for a second click on the launcher icon to hide the application is annoying. Sometimes it's handy to have an app that you want to look at for reference then close quickly. In GNOME you can click-read-click without moving the mouse and get back to what you were doing before. With Unity you have to jump through more hoops.
It does look like they've fixed a few of problems I had with Unity in 12.04. For example, alt+tab cycles windows on the current workspace only, and the default "spread" of windows behaves likewise. Sadly, icons for applications running only in other workspaces still appear, cluttering up the launcher wherever you are.