Well my first instinct is THE CRAFTING SYSTEM!!
I feel like farming for those shrines and then crafting a very sick item and selling the crafted item or the template of that item to other players is gonna be awesome (I am not sure if this is true but I heard apparently you can somehow save a part of a item or their affixes suffixes into like a shrine vessel thingy and then you can use that to craft a copy of that item or like guarantee some suffixes affixes appearing by using the said "template") Not sure if that is an actual feature in Sigma OR JUST RUMOURS?!? but I am excited for the upcoming changes for gear customization or variety!THE GRAPHICS
Because COME ON I love me some fancy looking interfaces and easier to navigate menu's and easier to read stats and text etc! Quality of life upgrades!!
Another thing is I realized that recently most bosses have the trend to slow down your breakpoints and movement speeds or just the overall speeds of your character by AOE's / DEBUFFS / AND OR / Speed themselves up by insane amounts (Making you feel weak against the boss OR the opposite Making you feel like the boss is incredibly strong
SAMAEL I am looking at u so hard right now
People love speed and fast paced gameplay = Fun Diablo 2 mod so I very much enjoy bosses that have Skill shots that you have the AREA SPACE to dodge/ AOE Skills that actually make you want to hide and in the down-time between of those spells YOU GO IN for thy kill!!
NOT Boss fights that randomly cast undodge-able one shot skills
without any type of skill rotation or pattern just going wild spamming spells on ur ass
while being incredibly hard to find any type of opening to retaliate or even get close to just one word MASSACRE
over and over and over!! I am definitely looking forward to the more skill based boss fights
EDIT: In the end what it comes down to being most important For me is... the Fancier graphics and the new big areas I can run around in having fun fighting bosses on more even terms and little convenient things such as the status effect icons etc thats all everything else is just extra