In that case the S4 should have been the S3.5. I had an S3 and when they announced the S4 I saw no reason to upgrade as there was no real difference.
I now have a Note 3 and a Nexus 5. This allows me to have the larger screen phone but also play with the latest versions as soon as they are released by Google.
I am really tired of seeing articles on Android sites about this phone and that carrier rolling out updates and I sit here on T-Mobile wishing I had an update.
For me, the S5 will be good because of the waterproofing and the camera improvements, these are 2 of my biggest complaints with current smartphones.