I think the lizard should have three seperate personalities.
*Curt Connors
*mindless-Animal
*The shadow self or dark side of conners that personifies itself as a sentient reptile
Curt connors is a good person and not a criminal/villain, this is the human part of him trapped within the lizards body and dominated by the other two personas. The part Spidey sees and wants to save. At times when the Conners persona surfaces temporarilly, the lizard will recognize people/places from his memories, become less hostile and maybe pronounce single words or sentence fragments.
When he enters his mindless animal phazes, he is just a savage lizard with no human personality traits. He doesn't speak, or attempt to communicate through body language nor show any interest or concern for human life or technology. This persona can still access some memories from connors brain, but due to limited reasoning ability, he can only use them for navigating and basic tasks.
The dark reptile side believes in its own superiority and has its own desire to survive that is independant from connors. In this state the lizard will also make calculated decisions that seem 'evil' and completely out of character for connors. This persona has a greater access to connors memories and can even exploit them enough to assemble machines and interact with tools, devices. While in this state the lizard will recognize people/surroundings and also be capable of saying single words, sentence fragments. But as I said he will not be Curt Connors at these times and has a hatred for humans.