What Critics HATED About Venom
2. They Didn't Understand The Comedy
Bafflingly, a lot of the reviews that came out earliest before the release (you may not have noticed them, given how tightly Sony squished the embargo to the release) seemed to suggest that their writers didn't know whether they were supposed to be laughing. They absolutely were, because the script has very obvious gags in that are designed to laugh, but it suggests a pretty big problem.
Perhaps it's because of the tonal issues early on or the identity crisis that smashes jokes against po-faced series portions, but it seems to have been a real thing for some critics that the comic thrust of the writing isn't obvious. They missed out, so it's difficult to suggest that there's any sort of wilful ignorance going on. Clearly, it's a problem with how the film transmits its own identiy.
And do you know WHY so many critics hated it? Well, there's a bit theory about what was to blame...