After playing a fair few hours of Black Ops 4 I'll say this.... It's pretty crap
The normal multiplayer is a mix between R6: Siege, Overwatch and Counterstrike but not as fun as any of those games. The class system is a good idea but the maps are too small and the game is too fast to appreciate them beyond randomly firing off your abilities whenever they are ready. The only mode that comes close to R6: Siege is the Search and Destroy mode as the lack of spawning makes it feel a little more controlled, but instead you find players running off on their own and spin shooting anything that moves. So it plays more like Counterstrike.
The other issue is the balance. Some of the abilities are way overpowered (like the dog) while others are complete rubbish.
Zombie mode is fun as always but it's not that different to every other zombie mode.
Blackout is good. It's a direct rip-off of PUBG but faster and more arcadey. The main issue I have with Blackout is the wait time. Some matches started within 10 minutes. One match I waited 2 hours to start. Others I waited an hour. While waiting you can run around the map and learn the map while testing out weapons but you can't shoot anyone and it gets boring fast.
Also, if you don't have an Xbox One X then don't buy this game. I mainly played it on the X but I tested it on the S for fun. On the S while playing Blackout the resolution is below Standard Definition. I couldn't tell the difference between a building and a person.
Overall I'd rate the game 5/10
Dead average multiplayer, long queue times, no single player campaign saved only by Blackout mode if you can actually get into a game.