Diablo IV is a massive game filled with all sorts of content, much of it quite challenging, but for your first playthrough, you can somewhat tailor the game's challenge level to your skill level by picking between two different World Tiers, which determine enemies' capabilities but also some bonuses you can benefit from.
While picking World Tier isn't a definitive decision, since you switch between them at will before starting a game or even during a game itself, picking the right one can make your time with Diablo IV much more enjoyable.
As mentioned above, Diablo IV lets you pick between World Tier 1 Adventurer and World Tier 2 Veteran for your first playthrough. The first is considered the normal difficulty, while the second hard. As such, the Veteran tier grants some bonuses that sound quite good on paper, such as a 20% XP bonus and a 15% gold bonus from monsters, which will help you reach the Level 50 cap much faster and upgrade your gear more often.
While experienced Diablo players may want to go for World Tier 2 for a higher challenge right from the start, if you're planning to truly experience Diablo IV, you will want to get to the endgame as quickly as possible, as it's only then that the game truly opens up with some additional customization options, such as those granted by the Paragon System and higher rarity items, that make the game even more fun. As such, you should blaze through the campaign in World Tier 1 so as to be able to quickly unlock World Tier 3 Nightmare and then World Tier 4 Torment. In addition, hitting the Level 50 Cap is extremely easy to do in World Tier 2 before you reach the end of the campaign, so enemies will stop scaling to your level, leading to diminishing returns in terms of XP points
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