This!
I was in the same boat. An Apple diehard. I've had every iPhone on launch day from the original iPhone. It was only recently that I just got "bored" with iOS from using it so many years, and it never really changing. I decided first to try a Windows Phone (Lumia 1020, just wanted to check out the camera really) and what a mistake that was. Windows Phone absolutely sucks. Then I traded the WP in for an S4 and wow, I can't believe everything I have been missing on iPhone. The options and things you can do on the Android are almost limitless in comparison. Apple is very proprietary and they don't open up a lot of the API's to let 3rd party developers change how the phone actually looks and feels. That's opposite on the Android phones, you can pretty much customize every last little aspect you can possibly think of on it, and I think that's awesome!
Make the switch, I really don't think you will be disappointed. I use "Easy Phone Sync" to sync up my music from iTunes to my S4.