The primary problem with Flash is all narrative and character based, but it really needs a visual overhaul next season. Not just the Flash suit that he's had since episode 1 (other than the white symbol), 90% of every episode in S3 seemed to take place with people standing around in that damn Star Labs set. I'm so tired of that boring plain concrete room.
Arrow upgrading to a visually impressive base in S4 didn't fix the problems of that season, as I said Flash's biggest issue is the writing, but Arrow at least had a sense of visual progression year after year, Flash has been static in that department since the pilot.
Assuming they make an effort to do a soft reboot and try to fix Barry's mess of a character and try to freshen up the show, they need to do that visual overhaul of everything too.