Okay, the dragon may only appear in the new dimension that is usually called "The Ender". There are portals in the strongholds that will lead to that dimension, which is probably the reason Endermen are out of their native world. This means Enderdragons might get out, but that's very unlikely. It may replace the Skyworld, although it's in the real world in the 1.9 Pre-Release 3, it's possible it will stay there, making 3 dimensions. The portal block for the Ender is in the pre-release, showing as a camera moving slowly in endless space.
I also tried the potions; I found out the reason there is so many potions is because there are 10 levels of each potion (in this case, Potion of Strength I, II, III, and so on). However, it seems that the itemcode for potions is not activated when you are not using 'em, but I don't know how that changes the game.
Endermen has also been made even harder and creepier, they can now deal 5 hearts a damage. They teleport when you shoot them with arrows/snowballs/any other throwable item (except for dropping items, of course). They drop an item called the 'Eye of Ender'.
You can enchant tools and armor when you get a certain level with exp, now serving a purpose. As far as I know, the highest level of enchanting is 20. This gives a cool effect to the armor and tools with a shining/glowing effect. To do this, you need a Enchanting Table (it also has a neat effect when it's near bookcases, the bookcases 'sends' information to the Enchanter).
This is all the info I can remember for now.
