They don't like that it's making pvp harder. Most of the people who are hating on it are young and grew up with games that were easy and forgiving. Minecraft used to just be spam click a zombie and you win. Now, it actually takes some strategy, and most of those kids don't know how to play like that,
This. I grew up on Doom and, later, Unreal Tournament. I rather like the idea of needing to put some effort into it.
Think, folks. Everyone hated beta 1.8 for a while.