I will break down every section.
Campaign - 6.6/10
The campaign was very weird to follow but did have some redeeming qualities, like bo2's campaign you can make custom classes but along with specialists things, adds more variety that I like. Story was hard to follow and felt very odd to just play. The approach they were going for was actually a pretty cool and good idea, but was executed poorly. Lets say that campaign was dreaming to be like mw2 and bo2's campaign.
Multiplayer - 8.2/10
For the most part it was fun with the new movement and specialists implanted into it, gun play felt normal with guns feeling smooth. The maps were pretty fun and it's noob friendly, first time I played bo3's MP, I was playing FFA and won. Not many guns were over powered except for some like the VMP and even the Kuda. Sometimes you may get in with rank 1000 prestige master kids who get their mom to wipe their butt after they take a dump. Movement can be a throw off for some people as well, and it's a little bid tedious and hard to master it. MP wasn't to bad and I enjoyed it for the most part.
Zombies - 99999999/10
You can't go wrong with BO3's zombies! people who say any other zombies mode is better, they are trying to be edgy and different. First lets talk about gobble gum. My dad has been playing zombies since WaW's nacht der untoten, and has only played up until TranZit. His opinion on gobblegums is pretty well, saying that it gives the player more of an approach getting into the game. You could choose a perkaholic and get everyperk on round 1. Or choose a classic gobble gum that lets you keep your guns after dying which he likes. Notice how I said "Choose"? yes it is completely your choice to use them. It is pretty balanced IMO. Now onto DLC's. Every dlc is great, Der eisendrache, gorod krovi, and the starting map shadows of evil. All those maps could be a top 5, and I would respect that. All these maps are so easy to learn and almost impossible to die under round 20. You can have the Der eisendrache storm bow and kill an entire horde with one shot, and on gorod you have the ray gun mk3, and on shadows you have the apothocon sword, and it is just so much fun to play. This zombies was very important for the story. Zombies took a run n' gun approach, but you are still able to hold out and camp with friends and get to high rounds. This zombies mode needs to be the best out of any one, and it is. Opinions don't matter, bo3 has the best zombies.
Black Ops 3 - 8.5/10
I would personally recommend to buy bo3 if you are a big zombies guy, and somebody who plays MP for a hobby. It's a pretty fun game.
Hope this helps for people still trying to buy this game in 2022!