I'm seeing the same things. I had no issues with the GM build but, since the update to the final build, I haven't seen an app update though I know some exist.
u genius, spent 5 minutes trying to get the timingwhen i first open the app store and go straight to updates i can see it switch from 'update' to 'open'. if i hit the button quick enough i can get the app to update correctly. once i do this, the rest of the apps stay as 'update' until i leave the app and come back in again. really strange.
Make sure you have enough free memory to update. I had error with 1.1g and cleared up a few hundred Meg and then it worked.
Thats what im thinkingI was having the same thing with 8.4.1. Updating to iOS 9 didn't fix it. Now it seems to have gone away on its own. The App Store servers are probably being taxed by the iOS 9 rollout or something.