Hey, I think you have an incredible game here that's especially commendable because of the way you've developed it all by yourself. Simply to see people comparing your project it to Battlefield is a testament to how good this game is. I've put a few recommendations/anti-recommendations down below:
Maps-I think that the best way for this game to get even better is to include more maps. I really like Dustbowl, it's a map that really allows the Sniper to shine and I think it was a great addition. For further map additions I think a D-Day-esque map or perhaps a WW1 trench map would both be greatly appreciated by the community, giving other guns like the Shotgun a chance to see some use, as it doesn't seem awfully viable compared to other guns like the Sniper at this point.
Helicopter-Don't change a thing. I see a lot of players here and on other sites complaining about how it's hard to control and the likes, but I wholeheartedly believe that the helicopter is perfect as it is. With a simplification of the controls or the momentum aspect of the helicopter it would lose realism and thus the whole feeling behind flying one. Along with this, the anti-vehicle weapons, in particular the lock-on rocket launcher, shouldn't be changed either, I find them to be at the exact right strength they should be at to give ground personnel decent odds at taking down targets like the helicopter or the tank.
Vehicles-I think that the current vehicles are really good, but a greater variety would be even better. My favorite part about the vehicles so far has been the way in which multiple players can operate inside of the same vehicle-really great aspect of the game. On this note, perhaps a hovercraft style vehicle would be a good addition to the game. Ideally, it would be able to travel across land and water, albeit with low traction, and would have multiple spaces for machine-gun operators in addition to a driver. Really though, any type of vehicle addition would be great!
Sidearms-Just some small ideas for sidearms, I think a silencer would be really cool to add. On pressing the relevant number, the silencer would be equipped to the main weapon, giving it that cool, silenced shot sound and eliminating the big flash of a gunshot. This would be ideal for sniping off enemy troops while staying hidden and would perhaps give a reason for the binoculars to be used more frequently, in order to search hills for a silenced attacker.
Woah, I got a little carried away there. Sorry for the wall of text. Once again, really great game, I love every minute of playing it and I hope you'll take some of my suggestions into account!