don't ask questions. go out and buy it now.
all the dogfighting is still there(although it's the diffuculty from 5, and not the hairy chested beastfighters from Zero) and there's plenty of it. there aren't as many aces as Zero, but there is a super weapon almost every 5 missions. the game is of epic porportions. enormous bomber fortresses that turn invisible and supernova stomp you, cities with laser rings, enormous radar placements, and so much more, all waiting for you to put the hurt on them.
you can finally upgrade planes. engine, wing, armor, weapon, and cockpit upgrades are avaliable. engine=better powerplant.
wing=modified wings for better stability and or manuverability
weapon=better weapon damage/capacity
cockpit=better flight systems(better air to air/ air to ground) and or beter HUD displays
the unlock system is pretty straight forward too. shoot the target with a star next to it.
all this considered, this may be the best PSP game of 2006. buy it now, then take the rest of the week off.