The Diablo 4 reveal was overwhelmingly positive for me. I'm looking forward to it more than Cyberpunk 2077 which is saying something. I love the atmosphere, addition of mounts, more vertacality, and opening up all of Sanctuary to explore.
The biggest downsides for me...
1. The wait... I sure don't want Blizzard to rush D4 by any means but it is going to be an agonizing couple of years.
2. No bow class reveal yet. I understand showcasing the Barb, Sorc, and the triumphant return of the Druid but I always play a rogue/ranger type. With crossbows in the concept art I imagine a ranged character is coming. The five character classes at launch means an archtype is being left out of the base game.