I pretty much hated everything they did to BO4. It all seemed like putting stuff in for the sake of putting stuff in because they've got to ship a game this year and bullet points on the back of the box. It was complication for the sake of complication not because it made the game any better.
They butchered Crash mode. The courses were too big, the destruction too spread out. You want to feel the effects your disruption not watch your car lying in a gutter while the crashing happens somewhere else. And what the hell was with the whole accelerating thing, they nicked from golf games? As I said complications for the sake of complications. The only decent addition there was the wind direction when you were in the air.
The races for the most part were okay, but once again most of the additions didn't add much, or even took away from the game. The whole 'Revenge' concept was appallingly implemented, when the camera cut away to your rival, it couldn't keep up in getting back to you racing fast enough. Just horrible.
For BO5 they need to strip almost everything out of Crash mode. Smaller crash junctions, focus on really intimate destruction (perhaps with next-gen the destruction could extend to the enviroments). Get rid of the pick ups, maybe keep the crashbreaker, but just one per attempt.
For the racing BO3 with BO2's boosting system would be ideal. Takedowns they should keep, the rest (like the rivals stuff and traffic checking) needs to go.
And the art needs to be the bold and beautiful style of the first 3 games, not the washed out look of BO4, which succeeded in making the course largely indistinct and personalityless.
I honestly couldn't believe, playing BO4, how a team that I'd previously thought of as talented and individual could have so spectacular balls upped their franchise in so short a time.