Pickup and play gameplay.
Loads of action.
Decent graphics and sound.
Multiple camera angles.
Lots of planes to choose from.
Plane upgrades, paint jobs and plane tuning.
Replays, medals and other unlockables.
Wingmen can't be controlled and are pretty much useless anyway.
The game starts with you in serious trouble the Leasath military has invaded your country, you're posted at one of the last remaining free military bases and they're coming. The aim of the game is to defeat the Leasath military by completing various missions such as destroy a landing party, defend friendly troops, destroy incoming aircraft etc etc.
Ace Combat X is a really fun game to play and has excellent pickup and play gameplay. You can easily put the game down for a few weeks, then pick it up again and get right back into the action without any problems.
One thing an action flight sim needs is action and this game has it by the bucket load. One second you're on your way to an objective and the next you've got enemies planes shooting at you, while SAM sites are shooting at you as well and you never know a few Aegis cruisers might have a go at you as well.
The game really shows of the graphical power of the PSP with the quality of the plane models, they look awesome. When an enemy plane flies past you the planes are recognisable and they really do look the part. There are different cockpit for each plane and they are well drawn as well.
Multiple camera angles ensure that you can see just how awesome the planes look, although when fighting you'll only really be using the heads-up-display perspective.
The sound in the game mostly excellent, explosions, techno/rock mix music but some of the voice acting is a little bit on the flat/dull side.
There are loads of planes to choose from in Ace Combat X, 40 in all including the well known F16, F15, F18, F14, F22, A10, MIG31 and well as some made up by the development team.
Missions actually play differently depending on what plane you choose and what ordinance you pick.
Planes can be upgraded with parts such as new wings, new ordinance, new engines etc etc. These upgrades change the way your plane handles and each upgrade has positive and negative effects. For example a new engine may increase your speed but decrease your stability.
When you complete a mission you can save a small replay of the last minute or so of the mission. Bragging rights maybe?
Medals and other unlockables are available for completing missions and certain achievements. This only adds to the replayablility that's already there.
The only bad point I can think of is you can't control your wingmen, I suppose this is because of the control schemes available to the PSP are limited by the number of controls. I don't know if controlling them would make them any better because they're quite useless anyway.
Overall this is a great pickup and play action flight sim. Even if you don't go for flight sims or action games this is throughly enjoyable and worth a purchase.