What Critics HATED About Venom
1. The Marketing SUCKED
There's a pretty big problem with Venom that has destabilised expectations of it and which undoubtedly has had some impact on the critical reception. The trailers suggest it's an R-Rated body shock horror movie that sees Venom arriving fully-formed. It is not that. It's not even close to that.
Instead, Venom is a pitch black comedy wrapped up in something else that SHOULD have been marketed more inline with Deadpool. That would have served the film well and made it a FAR easier sell, but you get the sense that Sony consciously did that in other to avoid direct, unfavourable comparisons. That's a shame too, because more confidence would have served this film hugely well.
The best thing you can do as a fan is to reject all expectations based on the marketing and go in with as clear a mind as possible. Don't think of it as a horror, don't think about it as a competitor to the MCU, don't even listen to what the cast and crew are saying about it.
Know this only: Venom is great when it's great and really does deserve your attention. Particularly for Tom Hardy's excellent, odd performance. If nothing else, that's worth the ticket price.