These strategies are derived from the official design descriptions of Diablo: Unbound. The game has not yet been released and no hands-on walkthrough exists, so treat them as reasoned guidance from the published mechanics rather than as tested advice.
The four launch classes fill genuinely different roles - Barbarian for melee pressure, Paladin for defence and support, Sorceress for ranged area damage, Rogue for mobility. In co-op, take the role nobody else has covered. In solo, weight the class that covers the widest set of gaps in the dungeon you are about to enter.
The Town Phase is the only window in which you can change your setup - skill upgrades, equipment and respec all happen there and nowhere else. There is no second look before the next dungeon. Decide your loadout fully before you leave town.
Loot from chests, Elites, side quests and kill streaks is randomised, so each drop is a push-your-luck moment rather than free power. Bosses hold the best gear, which means skipping side content has a genuine cost - but it also means a dungeon with a boss at the end has a known payoff.
Kill streaks are the most repeatable loot source in the game and the most reliable way to build XP and gear between bosses. When a run is going well, they are how you make sure the next boss is winnable.
Bosses have unique attacks, a lair and multiple combat stages, so the final encounter of each act is the real difficulty spike in the campaign. Expect to lose gear and skill cards the first time you meet a given boss and adjust afterwards - the respec is the intended correction mechanism, not a failure.
60-90 minutes per dungeon and 3-4.5 hours per act. If you have less time than that, play a dungeon rather than attempting an act.
Torment mode is scaled for endgame characters. Running it before the third act stalls your progression instead of rewarding it, even though it does hand out the better loot.
Gems sit on the player board separately from the chest, helm, ring, necklace and hand slots. A build that only equips weapons and armour is leaving a whole track of the board empty, and in a game with seven slot types that is a meaningful amount of power left on the table.
The design is co-op-first, so solo runs are longer and grindier. Your compensation lever is aggressive loot management and respec - treat the Town Phase as the main event rather than as a formality between fights.