Personally, I love the interface and how visual it is. I like seeing the album artwork that corresponds to the song I'm listening to, and I like how iTunes finds it for you so you don't have to do any work. But even if it doesn't, all you have to do (on a mac) is google the picture, and then drag the picture from the browser and drop it over the "artwork not found" icon in iTunes. Incredibly simple. You don't even have to download it or save it to your hard drive first.
Finding the artist you want is easy even if you're not used to the new interface. Just click anywhere in iTunes main window and start typing, it'll go to the name you're typing and highlight it for you.
And on a Mac, iTunes takes up either as much or less CPU than Firefox does.
I wouldn't use iTunes on my PC, because my PC is a piece of crap and can't handle it.
(Because it's old. Not because it's a PC.)
Even if it took up more, it wouldn't slow down my computer anyway. I used to be that way; "this one's better because it takes up less resources," but now I've realized that I only do one or two things at a time on a computer anyway. I don't even notice the difference when using a "heavy" program.
Like Finale. I know Finale is a CPU beast, but it doesn't slow my computer down. I'm not gonna switch to Sibelius because of something I don't even notice.