These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: The Su-37's you go up against in Operation Backhand. Moreso than any other highly-skilled enemy planes because your objectives require you to ignore them entirely and follow a complicated flight path to avoid heavy anti-aircraft fire, all while said Su-37's are continuing to chase and fire at you.
Fandom Rivalry: With Ace Combat, though this may be confined to a few silly YouTube comments. Generally, H.A.W.X. fans disparage Ace Combat's gameplay and visuals while Ace Combat fans disparage H.A.W.X.'s story.
Game Breaker: You thought QAAM's were bad in Ace Combat? The All Aspect missiles here, save for lower range than even the default Joint Strike missiles, are even worse.
Sequelitis: The second game managed to have less landmark locations and less flyable aircraft than the first, combined with almost no choice in the matter anyway, and subsequently sold much less than the first installment. Enemies are buffed compared to the first game so it's harder to curbstomp them by easily evading their missiles and getting an angle to shoot one of your own, but the effect is so pronounced that there is no longer any advantage to OFF mode and, as such, no point in using it.
The buffing of the enemies was probably inevitable, given the unrealistic way that a single fighter could cut through entire armies in the first game. It can still happen in the second game, but the enemy planes are now smart enough to dodge some of your attacks.