MMO systems
It's been written, on this site and elsewhere, that Diablo 4 is basically an MMO. There's certainly an argument to be made. The game has an overworld, gathering nodes, mounts, dailies, cities with multitudes of players, rep grinds, world bosses, collectibles, and probably a dozen other things that you wouldn't usually find in an ARPG but that would be right at home in the next World of Warcraft expansion POE currency trade .

A lot of these things are totally fine to have in your videogame, but have tension with the core loop that makes ARPGs great. Am I going to have to go around and click all those godforsaken Lilith statues every three months with a ladder reset? Are a bunch of annoying trolls going to grief me every time I try to take on a world boss? Am I going to get popups about Murloc pets in the new battle pass every time I open the game?

I hope not. I hope that Blizzard changes the fact that every time you level up, you feel like the game just got harder. One of the most satisfying things in an ARPG is hitting a brick wall, something you can't overcome, going somewhere else, leveling up or getting gear, and then coming back with a vengeance. With the overworld and dungeons scaling to whatever level you are, this just doesn't exist in Diablo 4. Everywhere you go, you bring the stronger monsters with you. This kind of system works in an open world game like Skyrim, but in Diablo, I just wanna blast hordes of monsters, get cool abilities and loot, and blast more monsters.

Itemization
I hope Diablo 4's itemization is better than we saw in the beta, and that unique items are important, flavorful, rare, build-defining items that aren't just more numbers. The gear in the beta was fine, as far as it went. Most of the items were forgettable, interchangeable piles of stats that made my characters stronger. There's promise, however. Some of the legendary affixes open up new playstyles, like the Blood Mist/Corpse Explosion build. The ability to imprint a legendary affix and craft something new is a system with a lot of potential, and the fact that it costs a lot of gold looks like a good early indication that they've given the economy some thought.

(Image credit: Blizzard)
I hope that trading in the game works out, and is robust enough to let players build their characters. It can be incredibly frustrating in an ARPG trying to farm for a specific item you need for your build. Trading can alleviate that by letting you farm other things (runes, exalts, Stones of Jordan), and trade for what you need. One of the major reasons I never circled back to Diablo 3 is that you literally still can't trade with people buy POE exalted orbs .