DUO is a distinctly recognizable shmup in all facets. However, what people will notice first will always be graphics and sound, and DUO is no slouch in that department. The graphics are simple but colorful, and use an array of cool special effects such as sparks and motion blur to accentuate the vibrant style. Everything is smoothly rendered and easy to recognize, which allows the player to focus on the game instead of trying to figure out what to do. Alongside this is the sound. While the in-game sound isn't all that special, the soundtrack to DUO is absolutely phenomenal and worth a listen to any electronica fan, even if they don't like the game itself!

The meat of the gameplay behind DUO is base around a single bar at the center of the screen. In much the normal standard, you kill enemies and collect the goodies they drop. If an enemy touches you, you lose both weapon and normal energy. Whenever you lose all your normal energy, the game is over, and whenever you lose all of a weapon's energy, it degrades to the next level. Enemies split into smaller enemies upon dying until you destroy the smallest form. Power-ups are plentiful, so don't be worried if you fail to get all of them that are dropping.

Unlike other shmups, DUO has enemies attack from both directions as well as sometimes change directions upon reaching the other side. Powerups also fall towards the center, making it a race to gather power-ups and accrue kills as fast as possible while still being aware of your environment. Speaking of power-ups, your two guns (one in front, one in rear) are upgraded separately. In other words, you can max out your front gun but have nothing on your rear guy. Whenever you attack, you also attack in both directions, so it's not too hard to kill enemies while maintaining your awareness. You can also shift yourself around so that your guns switch places. In fact, in one level, you do this uncontrollably!

Everything in the game is color-coded in very simple terms. For weapons, guns go from white to purple in terms of power, with white being weakest and purple being strongest. For enemies, however, this is different. Enemy colors determines what they bounce off. All enemies bounce off of the green walls, blue ones bounce off the center bar (blue wall), the red ones bounce off the outer walls (red), and purple ones bounce off of everything. White are the same as whatever their original ball is, except they are invulnerable for 10-15 seconds upon spawning. This easy color-coding of the rules is an excellent addition to the game, as otherwise it would be impossible to keep track of game behavior!

There are three modes in DUO. The first is Challenge, which dares you to finish 100 levels with saves every 5 levels. It's easier said than done, and a Challenge run from start to finish can last over an hour. Time Attack is similar to Challenge, except instead of a high score and 100 levels, you must finish 20 levels in the shortest time possible. Survival is simply a game of survive. Procedurally-generated levels and no break between the action makes this the most intense of all the modes. Keep in mind that all of these modes have 4 difficulty levels as well: easy, normal, hard, and psycho.

There is not a lot of customization allowed in the game, but you can fiddle with the settings a bit. There are three control modes (mouse, keyboard, joypad) for example. You can also fiddle with the motion blur and amount of special effects on the screen at once. However, the resolution is locked to 1024 x 768 and 32 bit, which can be off-putting for the people wanting to reduce resolution to get better performance. DUO is not a resource hog by any stretch of the imagination, however, so you can pretty much leave everything as defaults. Finally, if you so wish, you can move MP3s to the My Music folder in the DUO folder and set the game to p[lay your music instead of the standard music. Not many options, but the custom soundtrack settings are greatly appreciated.

DUO is not without its faults. For one, there are no online leaderboards, which for an arcade game of this nature can be a deal breaker for a lot of people. There are local scores, but it's not as good as competing online. Secondly is the rather repetitive nature. While there are three modes with a variety of weapons and enemies, they all play the same as the others. You can't control weapons beyond choosing to fire or not and your progression is strictly linear. Likewise, enemies never get more sophisticated than colored circles. It can drone on for those not accustomed to the particular kind of game.

DUO is a retro arcade game of absolutely stunning quality. While it may be a little inaccessible or unable to hold the attention of the more easily distracted, it definitely pushes the retro-remake design philosophy forward. It's slick, fun, streamlined, and not very large at all! DUO gives lots of fun in a small package, and is essential downloading for any freeware fan. You can download the game for PC through the developer's website. Instructions can be viewed in-game or in the instructions file included!

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