For what it's worth, I saw this thread and the reviews and was a bit worried at first. Watched some PS4 gameplay on Twitch and decided it wasn't as bad as people were making it sound. I haven't had any FPS issues and that's even in the destruction challenges where there's a ton of stuff blowing up on screen. Don't get me wrong, it's not 60 and it dips, but I haven't had the FPS impede gameplay. It's never gotten me killed, stopped me from completing a mission, or even made the game harder. I had way worse FPS issues with Fallout 4.
The only really annoyance has been the load times which really only impacts the challenges. It's really hit or miss too. Some challenges load fine, others take forever. One that loads quick will suddenly start taking forever. The suggestion of it being due to a memory leak seems pretty spot on. Whenever it gets bad I just restart the game. I've only had to do it at the start or end of a session so it hasn't been that bad. I imagine it'll get patched soon enough.
I've been having a blast with it.