I Quit temporarily and skipped Ghosts and Infinite Warfare. I never really liked Infinity Ward/Sledgehammer's map design. Too many blind corners and extra floors. I loved Black Ops 1 multiplayer, 2 was OK, even though 3 was getting too sci-fi I liked most of it (again, no rocket jumping please). 3 introduced Specialists which all had two special abilities on top of your regular class layout. One filled up real fast over time while your super strong one took a while to charge up. One that's in three and four is Battery, who's a lady that has a grenade that splits into multiples when thrown and her other ability is a grenade launcher you can temporarily use. The Specialist system was overall the best new thing added to the series but, just like the weapons you normally unlock, some can be overpowered and need occasional tweaking.