You might remember the release of D3 with rose-tinted glasses ?
Between the server issues (for a mostly singleplayer game!), the real money auction house, criticisms about the story and the visual palette, as well as a missing PvP mode, it had a LOT of criticism.
Meanwhile D4 somehow actually managed the feat of mostly stable release servers (though the online-only criticism still stands).
Hardcore dungeon zoomer fans used to current D3/PoE1 might not have been the target demographic here. Probably also why you unlock most skills so quickly (which is probably barely quick enough for most players to see, as 80% of them don't finish the campaign). And I find these complaints hard to believe, as after all, the top end playstyles still tend to be much faster, and different from early on thanks to how the paragon points and especially legendary aspects and finally unique items tend to transform the skills.
I found the last open beta of D4 so compelling (even more than the D3 beta) that I completely changed my mind about (not) buying it. They really nailed (again) that "Diablo feel" (whatever that is) that I have been missing in competitors'. I have also been surprised how well the dodge mechanic worked and how enjoyable it was. The campaign is good, the art is top notch, as usual.
Now sadly the way that the leveling works in the campaign is screwed up in that it's easy to end up with a too easy game if you start on non-easy mode and start doing even the slightest sidequest (which is a shame as some of them are great !). You would have thought that, after D3's evolution, there would be more than 2 difficulty levels available for the first half of the game ! I also don't understand why the seasonal mechanics have been pushed out of the campaign.
The worst issue IMHO creeps up late game (and even mid-game for the season 2) : item spam, especially for "legendary" items. (Listening too much to the most obsessive fans of the current D3 ??) Even worse, for some unfathomable reason, the legendary aspects don't even have unique icons to distinguish them at a glance in the inventory (ditto for dungeon sigils), which is frankly shocking for what is a Blizzard game with ridddddddddiculously long credits, and not some kind of small budget beta.
But then, just like D3 changed a LOT, I'm cautiously optimistic about D4 improving over the years. (The online-only / no mods issue will remain, and this lack of future is sad to see considering the man years of effort spent on it...)