Refreshing and enjoyable to play!
Ace Combat 04 is especially unique in its genre-mixing attitude when it comes to traditional air combat games. The style of combat is definitely arcade, in that the controls are simple and well laid out, and the planes don't handle extremely realistically, all of which lends itself to great playability by even the most novice of players.
However, Ace Combat 04 walks a fine line between simulation and arcade, by including (at the time) state of the art realistic graphics that even hold up well today. Cockpits are detailed and different for each plane, the horizon remains far away and realistic, exhaust and weather effects are superb, and explosions are good, though not great. Textures on the ground aren't amazing, but considering you're usually rocketing past it in excess of 600 mph, and miles in the sky, you probably won't notice, or care, since the landscape actually looks quite good from a distance. The outsides of the large selection of modern combat jets are very detailed as well, and weapon animations are superb. The frame rate, even when moving over a thousand mph with 30 jets in the air and hundreds of vehicles on the ground and weather and lighting and special effects contributing, remains at a rock-solid 60 fps, making Ace Combat 04 take complete advantage of the PS2's now aging hardware.
The controls are well mapped and don't really need to be changed from their defaults at all, although truly novice pilots may want to switch to a simpler configuration. It is advised that you leave it in default, as you are able to control your aircraft like a pro in no time with the added ability to use yaw. The learning curve doesn't really exist, because the controls are so intuitive. They just feel right. However, there is a short tutorial included. Every mission is different and interesting, and depending on the difficulty level you choose, can be challenging, but not unduly so. There is an adjustable difficulty setting that you choose at the beginning of your campaign. The main difference between difficulties is how much damage you can take and how much damage your weapons do, and how many enemies you must kill to pass. There is a time constraint on almost all of the missions, though assuming you are looking to just pass them, it won't be a problem. However, if you want to get the most money possible, with the biggest bonus, you must destroy a number of targets far exceeding the minimum, especially high-value targets, such as the "Aces," since they are worth more points and more money. In order to do this, it is a veritable race against time. This extends replay value as well, as there is a difficulty in getting the maximum number of targets while avoiding the time constraints, and enemy aircraft and/or SAMs and terrain.
Another nice feature is being able to start a new game over, while keeping all of your accumulated planes, weapons, liveries, and money. Besides all being different in looks, all of the possible planes you can fly all feel different, and you can tell exactly what would be best for your current mission based on armaments, speed, turning radius, how much damage you can take, and a whole host of other variables that are taken into account. Towards the end of the campaign, however, you will most likely end up only using a couple of the best planes available, and only ever go to the other ones for novelties sake.
The story is very well put together, and does a good job of engaging the player. The soundtrack in the game is likewise very good. Once the campaign is over, you are free to replay it at another difficulty or the same one, and try to unlock everything.
Invariably, you will have to spend upwards of 100 hours playing in order to be able to afford everything, since the different paint schemes cost as much as or even more then the original plane. In other words, you will have to end up shelling out upwards of 10 times what you paid for various weapons and aircraft in the first play through, to get everything that you can unlock. However, spending this much time with the game is a pleasure, as each mission is different in a great way, and enjoyable to play through again and again. On some of the longer missions, it can be frustrating to kill everything on the map (upwards of 300 enemies) and wind up crashing into a mountain because of a stall with one minute to go. However, once you become experienced this tends to happen less!
I highly recommend this game to anyone with an interest in flight sims, but aren't interested in babying their planes.