The thing about special effects is that in a world full of technology, directors and producers often forget about the plot and the development and spend too much time focusing on the special effects. A lot of movies recently have overdone it on the effects and the film has suffered for it. I personally didn't feel that Venom overdid it at all. There was nothing special about the effects but that was good because it meant that we as the viewer could focus more on the plot and the talent on display in front of us.
I've never really understood much about Venom. I didn't watch the third Spider-Man movie and I haven't read the comics so let's say that I am a complete novice. I enjoyed the movie. Venom is neither a good guy nor a bad guy. Venom is sort of a conflicted character who turns from good to bad but has no loyalty to the earth and actually has no loyalty to Eddie. They work well together and something about Eddie seems to work for Venom, hence why he stays but nothing is owed to Eddie and that means that Venom is free to behave as Venom sees fit which makes him neither good nor bad- a bit like Deadpool.

Venom is a solid movie and they will probably make another one to help continue with the Spider-verse and the MCU. Venom can also be a stand alone set of movies and even though there were a few cut scenes linking to Spider-Man, like the 'Guardians of the Galaxy' movies, it can be done as a stand alone and then brought together as part of something bigger when it needs to.
I hope that there will be another movie.