so the title's sakotage?

have a variety of game modes, unlockables, or achievements to work for to have an end goal and a sort of "reward system" to keep players happy and enticed to continue playing. vary the maps and the environments so not everywhere and everything feels the same. maybe add various hidden easter eggs on some maps just to add some nuance to it and make it feel more alive. play around with the idea of close quarters and long range maps so there's variety to play-styles and you need to change your loadout or play-style according to the environment you're in that way not every round will feel the same

Random maps Random mode ( like hard point , tdm , capture the flag , gun change every kill ) Add some fun events in long terms like snow ball fights

Make it round based, something to grind for, pvp is best, add variety and randomness in gameplay Note im not an actual dev

Grinding is extremely repetitive.

buffs or special items you can pickup around the map, or like the scorestreak in cod

I am not a fan of FPSs. I personally think the big ones on the market are often just attemtping to be serious, ended up in similar gameplay to each other. I dislike that. I like FPSs when they have gimmicks to them, such as Arsenal. Are you considering doing gimmicks? Something that could be quite fun is having natural disasters mixed in, for instance.

Add sabotage.

add a special feature for each game to make it easier or harder