Chaos Field is the fiercest of shmups to head the Dreamcast's way over the last eighteen months or so, and the latest game in a drip-feed of Naomi arcade titles to make it home. The game and its developer are little known outside of Japan, but in recent years the import buzz on Japanese arcade shmups has heightened, with a string of excellent games released. Add the fact that Chaos Field has appeared on the Dreamcast very late in the system's life, and you have a game with strong appeal to shmup fans and importers alike.

Like many modern shmups, Chaos Field rewards those who examine and explore the possibilities of the game system, rather than simply blasting away. As you explore, you will find that Milestone have produced a very intricate game of dualities. Departing from what you might expect, each Phase in the game comprises only timed boss attacks, with no lead-up. The fundamental task is to maintain a combo meter, which acts as a score multiplier, for an unrelenting series of these boss encounters.

Two special attacks are available: the offensive 'Lock-On Shot' (B + C buttons) spills up to 100 lock-on missiles onto the screen, and the defensive 'Wing-Layer' (A + B buttons) produces protective, shot-absorbant shields.

Two normal attacks are used for general survival. A standard rapid-shot attack (A button) is available for dealing damage, and there is a defensive, three-hit buffered slash attack (B button) to swish away bullets in your immediate path, and damage nearby enemies.

Two fields can be switched between at will (C button), which affect the ferocity of the enemy attacks and the colour scheme of each Phase. The order field will throw fewer bullets at you, while the chaos field increases the number of attacks and even the size of bullets. After field-changing the player is granted a couple of seconds' invincibility, but cannot field-change again for around twelve seconds.

Only special attacks add to the combo meter, and after a few seconds the combo meter resets. To keep the combo going, you must repeatedly use those special attacks to restart the combo timer. To continue using special attacks, a 'meta stock' gauge must be refilled by collecting meta items released when destroying enemy targets. The order field releases more meta items, which means the meta gauge stocks up more quickly, but the chaos field allows you to target bullets with the Lock-On special attack, which adds big numbers to your combo meter.

Putting all of this together, you should, whenever possible, switch to chaos field to use the Lock-On special attack, and quickly rack up a good-sized combo. The Lock-On attack must be carefully timed to catch the maximum number of bullets, but used sparingly enough to make the meta stock last. To replenish meta stock, you should switch back to the order field and collect meta items when a good number of destructible targets are available, while using special attacks to keep the combo going. You also want to dispatch bosses quickly enough that the time remaining rewards you handsomely, against your combo score-multiplier.

This may all sound hella complicated, but really, it isn't. Given a couple of hours' play time, manipulating the game to keep your combo going becomes second nature. You will begin feeling the various rhythms of keeping the meta stock filled, the combo meter increasing, and the enemy shot patterns at bay. It is at this point that the subtle interaction of the game mechanics really bites, and the player is hooked.

That is not to say this game is easy - bullets fill the screen from the first instant, and only become more dense as the player progresses. Ignoring the combo meter it is possible to hack your way through the first few Phases easily enough, but to really progress, and feel that adrenalin, the game system must be mastered, used, and abused.

Worthy of special mention, Chaos Field features one the most impressive, and extreme, uses of slowdown in a modern shmup. Some people may not realise, but slowdown in a modern shmup is normally intentional, and slowdown here is used to great effect. Launch the Lock-On attack at just the right moment in the chaos field and one hundred hell-bent homing missiles launch at once. The game almost stops just so that you can admire the perfect timing of your lock-on, and then gradually recovers the CPU time to carry on. Brilliant.

Visually, Chaos Field manages to impress, despite some seriously ropey textures, mainly by creating its own style. There is something slightly askew about the oversized craft, enemies, and bullets (and the genuinely inventive, unusual backdrop designs) that appeals. Put it next to a more celebrated shmup, however, and it will seem less polished - it is certainly functional, but possesses a certain charm. Adding to the charm, the music is of a very high standard. Chaos Field features a series of quality high-speed trance tunes, which suit the game perfectly.

While the game throws a brutal amount of harm at you from the very beginning, it avoids frustrating too much by offering so many choices of attack and defence. This naturally leads the player to learn the game system, and settle into their own style of play. Chaos Field also offers a choice of pilot to suit your method; Hal who is balanced, Ifumi who is the most manoeuvrable, and Jinn, the most powerful. There is a very long, rather than steep, learning curve too, as new techniques are explored, learnt, and shared. For example, in some instances it may be worth sacrificing a shield, which gains you half the meta stock gauge, but finding the right use of this technique, by balancing the loss with points, will take time to accomplish.

As with other recent Dreamcast games, Chaos Field is a straight Naomi conversion, lacking a level-select feature or gameplay demonstrations, although the game isn't harmed greatly by this. Chaos Field is one tough shmup, but a game that manages to offer enough variety, depth, and adrenalin-pumping moments to make it more than worthwhile. There are some breathtaking moments of sheer terror on offer here, which will humble and thrill even the bravest of players. Exploring each layer of this cleverly constructed game, as it unfolds before you, is a very enjoyable experience.