There were tons of things that were brought up in the World of Warcraft: Legion - Game systems panel, and there was one thing that was REALLY a major game satisfaction changer for me.
The huge changes to TRANSMOGRIFICATION.
Firstly they made the wardrobe. Here you will put all the items in your bag and void storage that you are soulbound will be added to your wardrobe. And it also shows you all the things that you CAN collect (greyed out) so people can go out and look for those items that they're missing (or for those obsessed completionists, go and hunt down every single helm that you can have for your armour choice).
The other bombshell news was that for every quest that we have completed, they will add the loot from that (whether you chose that armour reward or not) into the wardrobe. So 10 years of backdated quests, I will have all the outfits that I'd thrown away or disenchanted years ago!
The UI is familiar but with the wardrobe stuff on the right. This is a great addition and poor Mogit won't be getting much use anymore as you search for the perfect item transmog for your outfit.
Secondly, they added OUTFITS! You can even link your outfits to others so they can copy your outfits, and you can even customise them to show helm or cloaks, and now you can even choose not to show your shoulders too! AND you can have the outfits change as you change your spec too - now THAT is awesome!
Then he said there were 3 new transmoggable slots added. I was wondering what they were. Were they going to start showing rings now on fingers? But no, it was better.
Tabards, shirts and weapon enchants will now be in the wardrobe! How absolutely brilliant!!! My mind is totally blown over the number of bank slots I will now have!
Professions had some big changes. I'm not sure I quite understand it all, as it seems to me that crafted items are going to be very powerful alongside raid gear. I guess I don't mind that so much as long as the time sink into making one is as much as it is to kill a new boss.
However, the shared nodes for gathering is great. I like it in Guild wars 2 and it makes it better for everyone. I don't have a gatherer so it doesn't affect me.
A number of class changes were discussed to make the classes more immersive. Sub rogues sound bloody scary now, more stealthing and teleporting across the map to deal damage to some other target?? Melee hunters really are a thing, and disc priests will be mainly atone healing. Shadow priests are gonna be freaky with insanity and tendrils coming out of them and stuff! Guardian druids are going to be more tank bear face tanks instead of dancing ninja bear tanks.
Demon hunters and class halls didn't really have much of interest to me - because they're new, and I'm looking forward to seeing them anyway, so anything about them will be rather engaging to me regardless.
It's nice to see Karazhan being relevant again, Dalaran being a focal hub, and going to older areas to work on our artifact weapon. I guess I was always going to be excited about an expansion, but now I really have something to be excited about!