Just tried the demo... and man, I am so less thrilled about this game. Looking like a rental only at this point.
So OFF mode is still weird, and kind of nauseating. Yay.
 
So part of the HAWX thing is that you grind XP to unlock more planes, weapons, and skins. And the demo has XP. But for some dumb-fuck reason, you can't actually level up. Sure, you can unlock Lvl 2 after a few missions, but there is no opportunity to do anything about it. No way to upgrade your plane, or missiles. Retarded.
 
The bad part, is I came into it expecting to be able to, as I thought the original HAWX demo had this feature. I could be misremembering... but still. 
 
Planes feel sluggish and slow, enemy tracking is slow, and not nearly as snappy as it should be. The hud tends to not lock on to who you want it to, and will take its sweet time getting tone. Oh, and some enemies have infinite flares/chaff now, forcing you to get in close and gun them down, in a decidedly unfun way. yay.

I found the demo had the same problems as well. The planes can sometimes be impossible to manoeuvre as sometimes the ground and sky can look the same. And the 'infinite flares', I couldn't hit them with missiles but they could hit me, the demo didn't even tell me how to deploy the flares. The first mission of the demo was pretty crappy and too long, especially that refuelling bit. But the second was easy, at first, but then when the helicopters came into the picture, it was impossible. I took down one helicopter and then did barrel rolls to avoid missiles and then I crashed into the ground, slowing down didn't even slow me down enough. 
The 'cannon' takes forever just to hit an enemy plane, and missiles take forever to lock on (like you said). It was an all right demo, but I don't think I'll buy it .