Darius is one of those legendary, old school shooting games with features so distinct, that it made them entirely unique and unparalleled in the 80s arcades. Even more importantly, they retained and improved upon these features, evolving them from features to motifs, and thus created legacies. Take for example Gradius. Every Gradius title featured key elements: Vic Viper, the powerup system, infinite vertical looping, SHOOT THE CORE, endlessly looping gameplay at increased difficulties, and so on. Most if not all of these features appear in every game in the Gradius series, making any game in the series fully distinguishable from any other, seemingly generic shooter.
Darius (also known as Sagaia on some consoles) is another legendary title like this, where you control the trademark Silver Hawk ship, piloted by Proco and Tiat (as P1 and P2 respectively - their name spell out "TAITO CORP" backwards).
So what are the key motifs of a Darius game? There are numerous that I can name, and I'll try my best to name all I can. Let's start with the most obvious: the game runs in an ultra-widescreen mode. The original arcade cabinet of Darius and Darius II used 3 normal monitors, placed next to each other, to display the full playfield (Darius II had a dual monitor version as well). Way back in 1987, Darius already rivaled the width and detail of todays high definition sets. This feature was only prominent in the first two Darius games however; Darius Gaiden uses a regular 4:3 screen. It did so in the arcades and it did on every following home release - all of which were arcade perfect conversions.
Another Darius trademark is the weapon upgrade system. Originally, you had 3 upgradeable weapons (in brackets are the corresponding powerup colors): a forward blast (red), a vertical angled bomb (green), and the ARM which is the name of your shield (blue). (Further powerups include a grey point bonus and golden "smart bomb", hidden on various locations in the levels) If you gather enough powerups in a single life, your weapon systems will be upgraded to a new level. What makes this special is that these upgrades are permanent! And as such, not that easy to reach. Of course, they are rather effective upgrades as well. Darius Gaiden pretty much retains this system, with few minor modifications. The normal attack button fires both the forward blast and your angled bomb at the same time. Also, your normal attack level is not measured on the screen (it is still counted though, not hard to keep track of as all powerups have different visuals), and if you lose a life, it drops back one level all the time. Furthermore, the Silver Hawk is now equipped with a powerful Black Hole Bomb. This acts as a special smart bomb, which first sucks in every enemy and projectile on the screen, then unleashes a massive, vibrating, fullscreen plasma explosion. Very impressive, and also quite powerful, a very useful addition to the Darius arsenal.
But perhaps the most distinctive trademark of Darius is the visual style and its presentation, something present in every game of the series. Nearly all bosses - and some regular enemies as well - are based on various sea creatures. From crabs to ammonias to sperm whales to hammerhead sharks, even octopi are featured amongs the bosses, who all introduce themselves with the ominous "WARNING! A Huge battleship, -boss name- is approaching fast" phrase. All of these creatures are mechanical, or rather, biomechanical in design, with multiple destroyable sections (which limit or change their movesets). The biomechanical design is appliable to the whole series though, especially some of the backgrounds, but especially to the wierder boss designs. Darius Gaiden looks quite pixelated now, but it features just about every background effect it is possible to create on any hardware. Many levels look quite spectacular indeed. The bosses are easily the most impressive ones in the whole Darius series: they feature dozens of destroyable parts, and progressively morph as this happens. This is much more prominent then in other games, one recurring boss - King Fossil - for example, fleds its flesh in small pieces, revealing the mechanical parts underneath, while another boss, Ancient Dozer, turns from a tank-like dozer to a flying horseshoe crab. Another boss is so big that it takes up a whole level, both in size and gameplay: the Titanic Lance of Zone M, is a straight-shelled nautiloid with the size of 6 screens' width. The visual presentation of Darius Gaiden is, simply put, spectacular.
An experimental feature should also be mentioned. Darius II featured subbosses, Darius Gaiden does so as well - but instead of just shooting them down, you are now presented with another option. If you target their brains instead of their body, and pick it up as it falls out, you can gain control of these subbosses. Although they die quickly, and are not of much use (unless you happen to be severly underpowered, in which case some of them can be extremely helpful), its still quite fun to turn the opponents own weapons against them. This feature appeared in a more polished form later in G-Darius, where you could assume control of any successfully weakened enemy, with a set of "control ball" weapons.
Important to mention are the branching levels as well. Present ever since the first game, but showing your complete routes first in Darius II. After every completed level, you are given the choice between two alternate routes. For example, your first stage is "Level A". Once beaten, you can choose between continuing on "Level B" or "Level C", with the text "Zone A is over. We are now rushing to Zone B (or C if you chose that). Be on your guard.". You are hopping from planet to planet as you progress in the game. Furthermore, every route awards you a different ending (based on the final level you have beaten). Because of this branching level design, you need to replay the game multiple times if you truly wish to see everything it offers.
Darius Gaiden on the Saturn is a perfect port of the arcade game (may even be considered superior for its CD Audio soundtrack), and is easily one of the best Darius games. It's neither impossibly hard nor impossibly complex, the graphics are constantly changing, there are no loading times inbetween levels (only a minor if not completely unnoticable skip), and the music is just gorgeous. Imagine an interstellar opera with futuristic sounds, creating perfect moods for each and every scene you see as you travel throughout the galaxy. The grainy background graphics are balanced by the heavy use of special effects and detailed, creative sprites and incredible bosses. It's true that the gameplay doesn't offer anything extremely special (compared to other high grade Saturn titles), but if anything, this makes the game that much more underrated, because Darius Gaiden is truly one of the most fun shooting games on the Sega Saturn.