[Update #2]: Diablo 4's pre-season Patch 1.1 has brought with it a massive reduction in player power and survivability.
[Update]: Diablo 4's Season 1 will be launching on June 20th with new quests, items, boss and fresh start.
If you've been messing around with Diablo 4's endgame over the last few weeks, chances are you've noticed that that simply playing the game casually isn't exactly rewarding. This is especially apparent if you're trying to level up, since doing the incredibly challenging, high tier Nightmare Dungeons gives less experience than just roaming around a PvP zone and absentmindedly cleaning up elite pack after elite pack.
Thankfully, with today's Update #42677 this is now a thing of the past. I say this because the experience gain from killing monsters in Nightmare Dungeons has now been drastically increased, as has the experience awarded for actually completing the dungeon. While no exact numbers have been given, in my experience it seems to be a boost of around 80% or more. So if you're looking to push through to level 100, doing a couple of Nightmare Dungeons a day will get you there quite quickly, especially since you can now teleport to them directly!
The good news doesn't end there, however, as Update #42677 has also increased the amount of experience gained by opening Helltide chests. Additionally, the roaming Helltide bosses will now drop higher tier loot more consistently, so fighting them should no longer be a complete waste of time. I haven't had a chance to test these changes just yet, but if they're as serious as the Nightmare Dungeon ones, I have a feeling Helltides are about to become a lot more popular!
As a final note, the update has also brought with it a wide array of buffs to all of the classes and many of their underpowered abilities. There's far too many chances to cover in brief, so if you're interested in the specifics you'll find what you seek over at the official patch notes.
Enjoy, and I'll make sure to let you know once the next significant update arrives - hopefully one that will really shake up the current metagame and give us more viable endgame builds to toy around with.