So after the end of the D4 open beta all i have to say is, with this build of the game, it could be worse but could be miles better than what Blizzard let us experience. Its a very mid experience.
My tierlist for classes would be :
S tier - Sorcerer(ess) , ofc. The #1 class. This class is just bonkers, with its stacking power scaling. Teleport skill is the best movement skill and breaks CC, i mean... Easily the most mobile class, with an ungodly damage potential and easily the fastest dungeon clearer in the game. My favorite class in D2 is hands down the best class in the D4 beta, and anyone that says otherwise is just wrong. This class is just amazing and feels great to play with.
A tier - Necromancer. It feels good to play as necro, but anyone who doesnt like passive support based classes will hate it. This class does a TON of damage. In my opinion, necromancer is a 10/10 in damage output. This class is so overtuned and i love it. My second favorite class in D2 is also the second best class in D4 beta. Ok.
B tier - Rogue (melee) - This class in melee plays just like what you would want a melee barb that plays like a barb in previous Diablo games. Rogue has about the same damage as a barbarian, but with better survivability since youre not forced into melee ranges everytime even though you are focusing on melee. I know, kinda weird. Rogue is so fast, like brutally fast. It feels really good to play as a rogue.
C tier - Barbarian. Lowest survivability of all classes. Yeah, the class that is built like a truck is the squishiest one, especially since youre forced to close the gap into a really forced melee style as it makes sense for barb. His tools are really not sufficient to be comfortable at high end. Forced melee is a huge problem.
Garbage tier - Druid. This class is just really bad. Very low damage. The tools are there, but they are all really slow and low damage output. Needs a huge buff when the game goes live on the final build.
tl;dr - melee (except rogue because leech) sucks, casters are overpowered, nothing new - im expecting huge sorc and necro nerfs on launch and barbarian to top high end damage, and hopefully druid gets a massive rework because this class is like....not fun to play with.