The newest entry in the AC universe, with a streamlined interface, faster combat, multiplayer, and reduced difficulty.
First things first, the graphics have of course been updated quite a bit from the previous AC games on the PS2, the mechs themselves look amazing on a HD TV/Monitor, but the environments can be underwhelming at times, with a bit too many re-used terrain textures. The sound quality seemed decent to fairly good, though that has never been a issue with AC games, and hopefully will never become one.
On to more important matters, Armored Core 4 takes a big step forward for the series in terms of improving and giving a face-lift to the various Menu's and sub-menu's that consist of things such as the Garage, Assembly, etc. In layman's terms, it's much easier to buy parts and equip them, and several features of past AC games were removed to make this installment have a lower learning curve. This was done most likely in hopes of a surge of "new gamers" buying the game. Unfortunately what they did was in all probability anger some of the die hard AC fans with these changes to gameplay, Boosters are of less importance in this game, and their seems to be a reduced number of parts in total as well, allowing for less overall diversity.
As far as the single-player campaign goes, it is fairly straightforward, in each Chapter, there are multiple missions listed that you can accept, it's usually recommended you go in the order they are listed, but you can do them in whatever order you want. This game, like most other AC games, still doesn't give much advice on what types of equipment/parts would be the best choice, it leaves you to find out for yourself, so it's basically a guess and check system. The missions vary dramatically in difficulty, some being easy as pie, and some being crazy hard.
Unfortunately the Multiplayer, however awesome as the idea of AC online is, is a letdown in many ways, yes you can fight against multiple players, but for one, there aren't that many playing online at any one time, and 2. most of the people your going to go up against are DIE hard, fans of the series and have been playing one AC game or another for years, and you will probably find that they already have all the best combinations for parts and equipment, + are extremely skilled in AC4's combat. This all meaning that us normal players don't stand a chance in in Hell.
Overall, this game is a worthy title, if for nothing other than you can battle with giant mech's in High Def with a friend or two, and enjoy the great customizability.