In Night and Dawn, generally people could run in amongst them without much danger. They seem to increase in strength over time. By Day of the Dead, people are not so capable of breaking free from them once a zombie has hold of you. They are also capable of tearing apart a human being with apparent ease. In Day of the Dead, the zombies were strong enough to tear a man in half and tear a man's head off.
Zombies retain some knowledge or memories from past lives.
A dead body will rise within a few hours unless the brain is destroyed. Zombies appear largely incapable of normal speech. Some specimens have retains very rudimentary ability in this area. Some zombies appear to be capable of simple reasoning or have a limited intellectual capacity. The next step is to analyse in more detail the aspects of their physiology.