Customize! Mobilize! Vaporize! Battling giant robots has never been so great.
Armored Core 4 features an insane amount of customization options for your robot. You can build anything from a slow, heavy armored tank with a million missiles to a speedy, agile mech with a couple laser blades. You can customize color, accessories, weapons, boosters, and performance around a base mech that you also customized (including the head, legs, arms, and chest) and really create almost anything you want.
Of course, each bit of customization you do will have an effect on the overall performance of your mech. So you could give it the best armor and plating, but your mech would most likely be somewhat slower than a high energy based mech. Weapons and accessories will also affect the balance of your mech, so if you have a giant bazooka on one side, and only a laser blade on the other, you might want to put some stabilizers on a certain area of your mech to balance it.
Unlocking all the parts and such requires that you play through the story mode of the game, which really isn't that impressive and doesn't last long. There are some missions which last all of 30 seconds, others that will take 10-15 tries to beat. Each mission is set up so that perhaps one mech might do better than another, but no mission is impossible with any single mech.
Voice acting and sound are all great throughout the game, for how little there is. You'll hear your operator give you a quick briefing before a mission, and generally give you a bit of pep talk or further orders during the mission, but that's about it. The occasional line from an enemy Next, the more powerful enemy robots, pops up as well.
The game looks fantastic, boasting incredible weapons effects and terrain detail. Shooting lasers and volleys of missiles at enemies never looked this good. Explosions from said missiles and lasers also look fantastic.
There's also multiplayer in the game, allowing you to take your creations online and fight others. For the most part, it's a pretty decent experience, but it's no revolutionary multiplayer by any means.
All in all, a great game. Suffers somewhat from a lackluster story mode, but all the customizing and battling more than make up for it. If you like robots and explosions, you'll probably enjoy this game.