I'm not even sure Rebirth was much of the problem... it wasn't a GOOD story, and they were forcing retcons in... but the first couple issues I truly felt that was 'MY' Barry who was back from the Speed Force and wondering if why he was 'disconnected from the world around him... I think the character was okay there. When they randomly de-aged Iris and had him rejoin CCPD like nothing was wronge and changed his iconic costume into something 'modern'... ughhh... It went downhill fast.
I loved Mark Waid's Barry. I was a fan of his in the silver age, but JLA Year One and Brave and the Bold GL/Flash just reignited how much i wanted him back... i too felt REALLY disappointed with what they did