I guess I can see both arguments. On the one hand you do get a rather large game to explore for that $70 price tag in Diablo 4, it would be pretty silly of Blizz to give that away for free. Blizz is claiming 40-50 hour to hit level 50 and finish the main story, but that is not the extent of the game, just completing the main story and hitting level 50 will only show you like half of what the game has to offer, there will be plenty of dungeons left to explore in the end game, renown levels to earn and a paragon board to fill out for additional improvements to your characters skill tree and stats. Blizz says there are over 150 dungeons in the base game, and those dungeons can each take 20-30 minutes to explore from what I've heard from alpha testers, and you only are forced to do a set number of them for main or side quests, the rest are solely optional dungeons you can explore for both Codex of Power options for your build customization, and loot drops, including a higher chance of legendary drops from the bosses (each dungeon has a boss now unlike in Diablo 3).
The battlepass model seems to be for the core players, the long term players who will want to stick around for years to come, more so than for the more casual players who just want to see the story, maybe do some of the endgame content, and then move on to other games. I can understand Blizz wanting to monetize those long term players to fund the development of both future seasons of cosmetic battlepasses, but also to help fund the the likely singleplayer expansions that add new story and new playable classes. Diablo 4 is afterall essentially an MMO lite, complete with an always online persistent world where you can run into other players while out questing and group up with them or fight them if it's a PvP zone on the map. Between the two ways that Blizzard could have funded long term Diablo 4 support, a battlepass system, or a monthly payment like WoW, I definitely prefer the battlepass system.
On the other hand, it does look pretty shitty when you compare it to PoE 2, which is going F2P with a similarly large campaign to Diablo 4. They are using their cosmetics to fund the game being F2P to start with, unlike Blizz who is doing both B2P (buy to play) and cosmetic battlepasses.
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