I like the zombie hoard mechanic, zombies needed a unique ability to make them a threat and now they have strength in numbers, which makes sense for zombies. My one caveat is that baby zombies should be nerfed. They appear to be as strong as adult zombies which isn't fair as they're faster and have smaller hitboxes, which is especially annoying when they're on fire.
I don't like the change to skeletons. I can see why it was done, but it just makes meleeing them a chore.
Horses are neat, but their speed draws further attention to the game's annoying rendering errors. Mojang really need to focus on fixing the existing bugs in the game before introducing new features that make those bugs seem worse.