To me, none of these criticisms are unique to F4 (sloppy lines, final act, CGI, characters etc). In fact they are arguably more apparent in other notable films like Age of Ultron. I'm beginning to suspect that the baggage that preceding its release is having an influence in the minds of some.
Is this a defence of the movie? No, but when people are listing films like Batman & Robin and Catwoman higher in the eyes of critics, then doesn't that ring any alarm bells?
There are many things this film does wrong but equally it does some elements quite well.