I started with Operation Flashpoint when it came out, played it every day for quite a long time, left out Arma, bought Arma 2 and havent warmed to it because of the controlls and some other problems. I ve readed quite a bit about Arma 3 and decided to jump in. I did the showcases (well, havent mastered all yet :) ) and was pretty impressed. The controlls are very responsive and it feels good. As a flight sim enthuisiast I use TrackIR, rudder pedals and a joystick. Got it all working without problems.
Well, the helicopters are somehow weired in my opinion. The accelerate way too fast, climbing is most of the time too low. Also the HUD should stay at the front (or a crosshair). When turning my head the cross hair moves also and I cant aim with the rockets or the gatling.
Vehicle driving feels okay to me.
Infantry stuff has convinced me directly. The movement feels realistic.
Grapics are awesome. I dont have a high end rig but it looks good and performs very well. Sound is also quite good.
So the overall first impression is very good :)