1. The experience required to go from level 85 to 90 has been reduced by 33%
Mists of Pandaria has been called very alt-unfriendly, and while this particular change won't entirely fix that, it does help. Along with the changes to reputation factions -- the Shado Pan and August Celestials dailies are no longer hidden behind the gate of "Revered" with the Golden Lotus -- this will make it easier to get your army of alts up to speed to hop into max-level content.
2. Off-spec looting options have been added to bonus rolls, Raid Finder, Heroic Scenarios, and Mists of Pandaria quest rewards
My druid main self nearly cried in happiness at this announcement. I'm desperate to upgrade my feral spec weapon, but DPS queue times, by Elune! Allowing off-spec roll options is an extremely welcome change for those of us who play multiple specs on hybrid classes. The option will be accessible by right-clicking on your character portrait, where it will be available on the drop-down list.
Also welcome will be the ability to select off-spec loot as quest rewards. I recognize that, initially, the decision to show only the reward for your current spec was likely made in the interest of keeping things simple for players, but it was one of my least favorite aspects of Mists questing. In this day and age of transmog, many folks are interested in pieces regardless of their stats. Furthermore, for those of us who may quest in one spec but group in another, it was very frustrating to have to switch specs just to make sure we were getting the gear we wanted or needed from a quest. Overall, this change is one of the things I've been looking forward to the most in patch 5.3.
3. For PvP purposes, all characters now have a base resilience of 65%
If you, like me, have avoided max-level PvP because the gear-based barrier to entry just seemed too high to even bother, then this will be a welcome change. Patch 5.3 is bringing many PvP-related changes, and many PvP gear-related changes, and a lot of them are being made with the intention of making PvP more accessible to all players. I sincerely hope that these changes are successful in doing just that, because I would love to be able to do some PvP on my max-level characters without feeling like I'm just a sitting duck.
4. Low-skill miners and herbalists can now gather nodes in Pandaria
Been thinking of switching to a new gathering profession, but just can't stomach the idea of having to go back and farm all those zones all over the world? Well, good news everyone! (Real good news, not Putricide good news). You don't have to! You can mine and herb nodes right in Pandaria, and they'll give you some small amount of useable material. As you gain skill, of course, your yields will improve. How great is that?
5. The in-game support system now has a web portal direct to the Battle.net customer support site
This is a nice, convenient feature that will save us the need to flip back and forth between WoW and a web browser when we encounter technical problems with the game. It's a thoughtful addition, in my opinion, in that it's basically an addition for convenience. But we like convenient things, too!
Bonus 1: You can now transmog items in your bank or Void Storage
It's supposed to be a top five, but I wanted to sneak these in anyway. It's a nice quality-of-life change for the hardcore mogmaxers, and will save some gold for those of us who keep a Void Storage chock full of transmog gear.
Bonus 2: Lesser Charms of Fortune now drop off certain mobs on Pandaria, Isle of Thunder, and Battlefield: Barrens
Pretty much just as the note says! Now there are yet more ways to get Lesser Charms of Fortune, if you hate dailies. There are also more ways to spend Elder Charms of Fortune on the Isle of Thunder, so let's hurry and empty out our currency tab, it was becoming a little bloated anyway.
Happy patch 5.3, everybody!