Ubuntu's goal is to bring Linux to a wide desktop market, including people who aren't especially technically literate.
No one's saying that Gnome 2 wasn't great, but in this day and age, it looks dated. Compare the Gnome task bar to the Mac dock or Windows start bar. It's old - harder to get information from and harder to interact with. Half the people who run Gnome 2, and know what they are doing, install something like Docky or Awn, and get that functionality.
If you want an OS to be mainstream you can't expect your users to have to resort to 3rd party modifications for what is now considered basic functionality.
Unity is NOT more intrusive or distracting than than Gnome 2 (or really any other desktop manager). Gnome 2 has the top panel, bottom panel and windows borders visible all the time. Try hitting maximise in Unity, everything you don't need disappears. This is getting out of your way as a good OS should.
Additionally they're introducing window management features like the windows Aero Snap or whatever it's called. This is not intrusive (no new UI elements) and provide functionality which is great for productivity.
My only real problem with Unity as it is, is that it's fiddly to open an application with the mouse. Open the application menu, click on the small drop down menu, find the category, then find the app. That's too fiddly. But opening apps by hitting Super then starting to type the name is the best way to go anyway.
You might say "why not just use Gnome Shell?" Well that's a good point. But in 11.10, Gnome Shell will be available, and now we have more competition to encourage innovation. Is that a bad thing?
I think most of the criticism of Unity comes from the same old fear of anything new (take the new facebook, new myspace new anything...). Sure there are a few kinks, but they'll be ironed out as time goes by.
