One significant change in Venom 2 is in Carnage's character. It's shown that both Carnage and Kasady share an intense bond, and the two characters are inseparable in the Marvel comics to death.
The passion is entirely reversed in Venom: Let There Be Carnage, with Venom having the ability to use the love of Kasady for Shriek against him, which separates Carnage from the host.