Off to a good start,
Now characters need smoothening and polish of several areas. The first noticeable area (after hitting 25 and before), of the speed at which you target corpses and target enemies.
Drop rate & world boss:
I got 7 uniques from a world boss on a side note, item system should be considered a place holder for a better design. Granted 3-4 of the uniques came from some after drop, however, I do not see getting 7 uniques a challenge, I am assuming that these drop rates are purposeful for the beta. Should level 25s even be able to defeat a world boss? World bosses are normally for max level or high level folks, and rares or elites or super elites are for these lower levels of 25, etc. Hmmm pondering a design without a solution idea.
Necromancer skill tree design:
Skill tree is a bit make or break, you basically just plant a brick for curses, kind of a blocky feel. For a working example, it feels like the auras and effects of curses in D2 were perfect, you could clearly see which mobs were cursed vs not cursed. Some of the skills in the tree are a bit useless.
Skill tree design:
Skill tree design feels like working in paint, it’s super enlarged and has limited zoom. Skill tree has to be zoomed in and around to maneuver, I have no way to see all of my skills at once! Putting only 1-5 points in a skill is like buying a brand new race car that has a speed governor, some skills should have a larger scale of increase, example Frozen Orb in D2 you could max to 20 with bonuses going over +, we could go hard on our favorite skills, it was never limited to 5. Skill image icons are a bit similar, you can’t really tell what you are putting skill points in until you hover, they need redesign in terms of looking more unique. Make sub skills useful again! 
Usefulness of skills:
Some are just not useful, there should be more of this is a bonus to a skill tree build and less of 100 different things that can happen. If 100 different things can happen, then that would require 100’s of build combinations in design. Granted, I am all for more combinations as it feels like in some games you have to choose this simmed design and no other pathways are good enough, D2 did a good job of surprising players with investments of skill trees. Ideally, there should be some combinations of skills that make players happy! I really liked in D2 how some skills appeared to be not so powerful, then at max level, you could make those skills come to life with good skill tree combinations! I would say that essences need a redesign. Can essences stack? Why use slows or stuns, daze or knockbacks at all when your melee have a thorns build? So build swap requires inspecting each melee on your team? Asking to be sure? It seems like one players build should not directly counter another players abilities. Granted, there are some obvious counters, however, like I said anything of CC is disabling a barbarians ability if they are built for a thorn or absorb style build. I like CC and want to see these skills work together a bit more! Another design that I do not have the answer to.
Merchants:
It feels like you can do almost everything at level 25, what’s the prize at max level besides paragon? I am not sure on specifics it just feels that way. Uniques a repeat of max level, same few essences, etc. Other considerations, why salvage aka disenchant vs sell? So many different items from salvage with same value. Why so many different salvaged results with same value? Hoping that the salvaged results end up having a purpose, value, and player desire to get each. Item upgrades are a bit low, same materials for upgrades wasted on low replaced unique and then you have no mats left for higher levels? Overall, just consider if these designs currently make sense and how to make them more needed or desired by players. Essence is really bland, you don’t feel of anything rare or unique having value, it’s just add the same 1-x essences to any item, so all that mattered was stats on the same slot item of any value? Why have rarity then at all if that’s the case. One of the best things about D1/D2 was the chance to find something rare item wise, seeing a player with items that not everyone has, or a set, and finding a valuable unique, etc. There’s just no point in any value in the current system, you’re either on or you’re off! This does not make sense. One of the heat maps of previous D1/D2 was the amount of time that players grinded bosses using magic find was because what could be found was a large variety, not class specific at all, publicly shareable, and rarity into the .00000x1 % chances of dropping. Finding something like a Ber or Zod rune would make you rich! I don’t think that there’s any point to grind yet, you just get your 5-10 essences and you are done. Items dropping with a level cap for the same unique is just not a thrill. Uniques always had a set level cap. Chance for a 3rd stat and socket was the rarity. One merchant that is pretty good is the stat replacer, however, there are better ideas to make these tools not so necessary and return emphasis to magic finding once again. Design should consider how rarity scales and look at the current system how it can be improved even if it means ripping the code guts out and going for a goal that has a valuable result to players.
Final thoughts:
I am hoping that much is placeholder and I fear that the design efforts needed will be very time impacting before June 6th. It’s going to be an actual challenge to get Diablo 4 ready by June! I am hoping that the improvements get put in even if it means patches or release delays for the better. I am sure that fans would rather complain about waiting longer than getting a faulty design. -Gotta shift the weight of what’s in front. (Analogy of priorities).
Best Regards,