Changes in portrayal of Zombies.

I think we all noticed. The "zombies" in the first movie were absolutely beautiful. So much so that I would even hesitate to call the zombies, but more so, zombie like. They simply walk, and stab people with knives. These guys even TELEPORTED at times. Do we all recall the scientist in the first movie? He sees the zombies feet from underneath the temple, yet when he looks up, nothing. Also notice how they zombies do not eat people or really make any sounds. Just the occasional mumble.

In the second one, they are more or less the same, except far more aggressive. Running, yelling, etc. Not exactly sure was up with the zombie lady.

And of course, our 3rd movie. First zombie we see is your typical zombie. Its a cannibal, though its oddly trained like a dog. It does not attack other nazis. And of course, the strange hulk zombie.

So what explains these changes? Are all these zombies in the prequel simply prototypes leading to the zombies in the first movie with supernatural abilities? These may have been damaged when they temporarily shut off the machine in the first movie, thus we have the more aggressive like zombies in number 2
Thoughts? Add ons? etc