TBH? CS:GO's Black Zone BEFORE the update. Rn it's just super meh =.= Like a crappy rip off of apex.
But before, there was so much strategy and nuance in every step you took while playing, ESPECIALLY in solo mode. Every gun is loud as fuck which means that if you aren't careful you're going to get 3rd partied instantly, every gun comes with/has very little ammo to use and you have to be very careful with when you shoot and why or else you'll run out of bullets mid-fight. Every choice to loot an area or buy items via the Drone is a risk/reward you need to carefully decide on, and the drone mechanic was awesome too. Looking at the minimap/shop effectively stunned you, leaving you venerable to death. Not to mention the default CS mechanics of having to sneak, having to actually aim well or you miss ALL your shots, etc. It was one of the best battle royals I ever played!...
...until they turned it in to discount Apex Legends =w=