Cons.
-The AI is garbage, first time I ever see someone call the AI in Arma smart.
-controls are a joke, some of the keys aren't even working anymore and are just left overs from previous games. The game shouldn't be that clunky to play, they don't even have to compromise on anything. That's just bad design on their part.
-No tunnels, or underground structures... Come on BIS, it's been fifteen years.
-performance are crap, single thread engine in 2016. Actually they managed to give AI pathfinding its own thread, but that's minor.
-physics and collisions are really glitchy. Like really, I still get killed maneuvering in rocky hills or in ruins when I don't get thrown away exiting a vehicle. The smallest collision between a vehicle and environment can flip over your vehicle. PhysX can do a lot better than that.
-lack of vicinity search in inventory is painful, when you want that RPG on the ground like right now but inventory keeps not showing it.
-way exagerated fatigue and sway features adds to frustration, this is just garbage. I understand they are proud and want to showcase fancy features they added. But this is just bad.
-damage model is such 5.56 virtually useless even in face shots, 7.62 underpowered. That thing will suck the fun out of any PVP game. Especially when launchers and weapon are unpenetrable as well.
-armor and damage model of vehicles is a joke. I hope they'll get rid of that hitpoint system sometime this century. This isn't good. Plus some destructibility when vehicles get hit wouldn't be luxury in this day and age.
-The setting is bad, please ArmaIV back to its Coldwar roots I hope.
Animations are still lacking. Unlocked reload animations, different magazines on models, last chamber in chamber would be nice...
Pros.
Most great solo/coop tactical shooters have been killed by Taketwo and Ubisoft throughout the years so Arma is the only one filling the gap.