One of the largest changes to the game was the talent trees and points. There are no longer 51 total points (now 41) that can be used. The another change is that you can only choose 1 talent tree at a time. Each tree has a total of 31 points available, and it must be full before you can place the other 10 points in the two other trees.
Due to this change you do not receive a talent point at every level either. Once you receive the first, every point thereafter will be available on the odd number levels (13, 15, 17, 19, etc.). You will still train on the even numbers, but they are few and far between. Definitely something to think about while leveling.
Mastery Rating and Reforging
There have been several changes to the various stats in the game. For instance; Resilience is gone or in Blizzard's terms; "It no longer helps reduce critical strikes." Also, Mastery rating has been introduced and will provide each class with certain stats. This is also based on talent specialization.
Anyone who is at least level 70 and has gear or weapons at a 200 item level or more can utilizing the Reforing process. It's important to understand that even though you can add additional stats to the item, it can not be the same thing. So basically, you can not add +25 agility to a two-handed weapon over top one another.
In the past, World of Warcraft only allowed Paladins and Warriors to wear plate. Those individuals who were tanks ended up paying tons more in gold for repairs. Blizzard decided to make it fair for everyone and give all cloth, leather, and mail the same durability points as plate items.
When the 4.0.1 patch was first released, people were scrambling around the auction house paying overpriced amounts for glyphs. This was due to the format changing, which now now allows 9 different glyphs to be used by level 75.
You receive your first 3 glyphs at level 25, the next 3 at level 50, and the final 3 at level 75. It's also important to understand the types of glyphs have changed. You will now have the ability to use 1 Prime-glyph, 1 Major-glyph, and 1 minor-glyph for each section.
They have also added Vanishing Powder to the mix, and one must be used if you want to change a glyph in your tree. However, do not pay the huge prices in the Auction House, because you can find it at your nearest Inscription supplies vendor.
The best part about the 4.0.1 patch is that the game was completely overhauled. However, it also means you have to spend some time re-learning your class. Whether it's the abilities, rage, mana to focus, or anything else, understanding your toon will take some time.
The good news is it brings new life to the game right before the WoW Cataclysm released date.