Venom has three actual weak points, the most easy of which for Spiderman to take advantage of is his unstable formation when high frequency sound hits him.
That being said, Venom is interesting simply because he knows what most villains do not; Peter's identity, his location, his habits, essentially all of his life and the memories it has produced since the symbiote originally latched to Peter.
Also Venom is not a person, but an entity, a union between Eddie Brock, who already has a vendetta for Spider Man, while the symbiotic power he joined with resents Peter Parker as a person.
Despite the anger, Venom in most stories eventually becomes not so much a hate fueled duo, but just an angry thing that tries to do what it believes is right, but will do whatever it can to fuck Peter Parker / Spiderman's shit up, yet will join up IF need be.
If Eddie was smarter, yet has less charisma and emotion, he would have killed Peter by now, but there is a strange shred of humanity found not only in Eddie, but even his alien counterpart, which is funny, seeing as the original point of the symbiote was that it was not alive, and when it finally was shown to be alive, nobody cared, for it appeared to have non-human emotion, when in reality the opposite is true.
Venom has taken other hosts, and do not even get me started on the whole Carnage bits, but the fact of the matter is that Venom is a villain that plays itself, and the writers are the ones who either set Villain up as a great character, or just a flash in the pan villain based off nostalgia.
