One of the first things that grabbed me about Diablo IV is its downtrodden world and intense atmosphere whenever its main antagonists make their presence felt. The main hub world of "Sanctuary" and its five main locales offer a nice variety of biomes that do a great job of reflecting the loss of hope and immense despair humankind is experiencing. It's easy to feel bad for everyone and seek out any side quests you can in order to give them just a sliver of happiness and satisfaction that'll lift their moods just a bit. Running around muddy forests, snow-capped mountains, and other weather-effected environments meant I got engaged in battle with a wide variety of enemy types, cleared out procedurally generated dungeons with plenty of loot to uncover, and random "World Events" that serve as fun detours from the main objectives at hand. The overall art design and music that backs your continued journeys through every part of Sanctuary go hand in hand with the gloomy influence left behind in Lilith and her followers' wake.
Speaking of Lilith, she stands out as one of the most imposing villains I've encountered in gaming in quite a while. The story revolving around her unwelcome return kept me intrigued from beginning to end - trailing her whereabouts means I came across a village full of cultists, legendary heroes who've become crazed advocates backing her evil deeds, and crazy revelations that expand upon the epic conflicts that have entangled angels, demons, & humans alike. Diablo IV reverts back to the super dark and hopeless feel of the themes present in Diablo II, which is something I know most diehard fans of the series greatly appreciate. From a graphical, musical, and storyline standpoint, I'm enamored with everything Diablo IV brings to the table.