I used to be very down on iTunes. But then I realized a couple of things. First, I was still using Windows XP — not currently, but well after the release of Vista and Windows 7. So, that's one thing. When I switched to OS X, general performance was much, much better. That's not to say that only people on XP hate iTunes, but considering how long MS kept XP alive, I suspect it was a factor. (Also, Vista just plain sucked all around.)
Second, I realized that iTunes is in part a DRM management app. And that's mostly due to content license holders — the recording industry, the MPAA, or whatever. Basically, iTunes handles every licensing agreement that has been laid down on digital content ever, behind the scenes, so that you don't ever have to deal with it. That's something that changed iTunes from its original inception, before the iTunes Store, when it was just a media file manager. It's also something that can't simply be eliminated. You really do expect to be able to listen to every song you've ever purchased for the past 10 or more years, on any computer or iOS device.
I do think iTunes has become relatively unintuitive, especially for newcomers. But the basic functionality required of it makes it difficult to change. Like, it should be able to back up "content," which includes apps, app data, songs ripped from CDs or purchased from almost any digital distributor, photos, videos, movies, text messages, and now health data. But it still functions as a way to use and buy media content.
People frequently bring up the idea that it should be split into multiple applications. And I believed that for a while myself. But I don't think that would make it easier to use. The main legacy issue that keeps iTunes the way it is is actually something specific — the relationship between mobile devices and PCs.
This is something that Google doesn't have to deal with, because they got into all this very recently. But it's something Apple has had to confront in multiple ways. For instance, back when the iPhone 3G was released, they issued a critical patch for iOS. But many users didn't know about it, because they never synced their iPhone to a PC. That was the first time Apple had to deal with the fact that smartphones became autonomous devices and were no longer PC accessories. Apple has slowly adapted, by introducing iCloud, iTunes streaming, etc. But they have to continue to support everything else they've ever done.
There isn't an all-encompassing solution for this situation in general, IMO. For instance, not everyone wants to stream all their digital content from the cloud all the time, if they have caps on internet usage at home. Not everyone wants to back up personal data in the cloud. A lot of people who get a set-top box want it to access local files as well as content from every possible online distributor. Etc.
So some of these problems aren't going to go away. But it's worth realizing — there are a lot of iPhone and iPad users who have never synced their device to iTunes and simply don't use or even think about iTunes. In a certain sense, iTunes has become optional. It depends on when you got into the game.