Sega's Quartet seems to have come about by taking Midway's Gauntlet and turning it into a side-scrolling shooter. While the basics - the four player simultaneous action, the draining life-meter, the monster generators - are all clearly inspired by it, Quartet reworks all of these concepts into a drastically unique title.
There are four different characters to play as, each with their unique weapon - Lee, clad in blue and sporting a distinctly 80s mustache, has a wide beam; Joe, wearing yellow and being the generic good guy, has a "speed gun"; Mary, the sole lady and clad in red, has a bazooka; and Edger, with a bald head and keen visor, wearing green, wields the "miracle gun". The quartet of warriors has been sent to a space colony named Zero-6, which has been taken over by space pirates. The goal is each stage is to find the boss monster, kill it to obtain the key and unlock the door to the next area. In the first few stages, the boss can easily be found hanging out right by the exit, but in later areas it usually takes a bit of searching before you can find the monster. The levels are fairly small though, and only scroll horizontally, so if you stumble across the exit before the boss, it's just a matter of doubling back.
The stages are also littered with power-ups. The most common allow you to jump higher, walk faster, or even grant you a jet pack to fly, but you'll also routinely see bouncing colored balls of energy. As you shoot them, they'll cycle through four colors - if you grab it when it corresponds to the color of your player, then your weapon will be strengthened. It's best not to get too attached to these powers, though, seeing as you'll drop most any time you take damage, and you lose them when you go to the next stage anyway.
Beyond the four player simultaneous action, there are numerous traces of Gauntlet's inspiration, although they've been tempered with. The stages are filled with enemy generators, which consistently pump out bad guys, but there's no way to destroy, or even damage, them. Your characters' health is determined by a numerical gauge, starting down at 9000, and depletes slowly over time, as well as when taking damage. However, the counter is actually quite slow, and since Quartet is never as relenting with its bad guys as Gauntlet, it doesn't feel like it was cynically designed to gobble your quarters as fast as possible. Ultimately it's made redundant because there's an invisible timer anyway, which will send a grim reaper after your characters if you take too long.
As a single player game, Quartet is only barely interesting. The largest annoyance is the amount of time it takes you to recover from a hit, plus the need to retrieve any dropped items, but otherwise it feels rather rote. On the other hand, these mechanics make sense when put in a multiple perspective. Obviously, the dynamic changes completely when played with two or more people, which, as the name implies, is obviously the way it was meant to be played. There's a unique cooperative/competitive dynamic that's constantly changing, because while all of the players have the same goal in common, they're also all competing for score. Throughout each stage there are score items and multipliers. Furthermore, at the end of the stage, everyone is ranked according to performance, with the player who opened the door gaining the most points. While you can't directly harm other players, you can screw them up by bouncing off their heads, potentially screwing them up just enough so they can get hit by an enemy and drop their key, so you can grab the glory for yourself.
Visually, Quartet is decent looking, though the handful of environments - outer space, cave, ruins, ducts, and base - are recycled throughout. The sprites are small and a bit dorky, but some of the boss designs are a bit amusing, especially the one-eyed, banana-hammock clad bat creature. Similarly, the music is catchy, although with only four or so tracks played throughout the whole game, they can get repetitive. The punchy FM synth of the Quartet main theme is on par with other Sega arcade tracks of the time. Also notable is the rap theme, where staticy voice samples stutter out "S-S-S-S-S-SEGA!" It's not pleasant to listen to, but remains amusing that in 80s "what on earth were they thinking" sort of way. A few of these tracks were also carried over Sega's Spider Man arcade game. The soundtrack was provided by Katsuhiro Hayashi, who also did the music to SDI, Gain Ground, Ashura (Rambo First Blood Part II/Secret Commando), Hokuto no Ken (Black Belt), and worked with Koichi Namiki on Galaxy Force and Super Hang-On.
Without the arcade (or online multiplayer with MAMEHub) experience, it might be hard to see what's so interesting about Quartet. Four player games eventually exploded in popularity thanks to Konami's Teenage Mutant Ninja Turtles, but the game and its descendants were all beat-em-ups as opposed to action-platformers, and none really had the same competitive thing going for it. Even now there remains nothing quite like it, as sort of evolutionary dead-end that remains an interesting experiment in multiplayer gaming.
There is also, technically, a Quartet 2. In the grand Sega tradition of releasing "sequels" that are only minor variations, this is a conversion kit that is basically the same, but instead only allows for two players rather than four, and each player can pick their character, as opposed to being assigned based on which joystick you pick.
Quartet was released on the Commodore 64, Amstrad and ZX Spectrum, published by Activision and ported by Core Design. The Amstrad and ZX Spectrum versions are similar, but the Spectrum one is slightly more colorful. Both are incredibly choppy and barely playable. The Commodore 64 version is rather slow, but the levels still suffer from the same incredibly boring design. The music is a hacked up and drastically shortened version of the theme song, which had the potential to be decent if it weren't so repetitive. Despite the presence of four status indicators at the top of the screen, all versions are two-player simultaneous only. There are also only fifteen levels in total. Needless to say, none of these are particularly worth playing.
Quartet was also kinda-sorta ported to the Sega Master System, although it's really more of a sequel/spinoff than anything remotely faithful to the arcade. Four player simultaneous play is impossible on the platform, so the game's been scaled back to two players at the same time. Lee and Joe are gone, leaving only Mary (now with a ponytail and a miniskirt) and Edger. The Japanese version is known as Double Target: The Sleeping Cynthia, with the subtitle referring to the sleeping-in-statis space princess your characters are to be rescuing. The American and European versions keep the name Quartet, making its ties to the original arcade game more evident, even though that name doesn't suit the conversion at all.
There are only six levels, a massive step back from the thirty-two of the arcade game, though most stages consist of two or three areas with different background tiles, as well as unique bosses. However, you need to find the five (not quite hidden) stars if you want to access the final area. There's also an actual ending now, compared to the arcade game, which looped infinitely. You now have three lives as opposed to one, and your energy starts at 10,000, though it counts down much more quickly. There are also bottomless pits, which of course mean instant death. Though there are a few different weapons, the bouncing colored power-up orbs are gone, and many power-ups have been removed. The monster generators are technically missing, though now enemies simply respawn randomly around the screen.
Technically it's a decent enough rendition, because it realizes that the arcade game just couldn't be duplicated given the hardware, and just sort of does its own thing based on the template of the original. It's not an amazing game by any standards - even as a two player game, it pales next to something like Contra on the NES, which is its closest equivalent - but it's a more fun as a single player game than the arcade version, which says something.
Other than the name change, there's one other curious alteration between the regions. In the Japanese version, Mary looks similar to the arcade version, with black hair with bangs, tied in a ponytail. In the American and European versions, she now has wavy, medium length brown hair. Presumably this change was to make her look more Caucasian, although even following that line of logic it's a bit nonsensical, because everyone looks like manga characters anyway.
The only arcade perfect version of Quartet was released in 2005 for the PlayStation, as the 21st volume in the Sega Ages Line. Dubbed the Sega System 16 Collection, it's an extremely accurate emulation, with numerous screen display capabilities to run at 240p, 480p or 480i, with the ability to add in scanlines. By default it uses the Quartet 2 ROM set, but if it detects a four-player adapter, it will run the original Quartet. Also included is a bunch of supplemental material, including a short instructional manual, as well as both regional versions of the Master System port. It's a nice package, though some sort of online pack would've been nice. The disc also includes S. D. I. (more known for its Master System port, Global Defense), with all of the same options. Compared to other compilations, featuring only two games makes it feel scant, especially for these two games which weren't entirely popular, but they were selected as a result of an online poll held by Sega. Around the same time, a soundtrack CD was also released containing the music to both games.
Quartet has not been entirely forgotten by Sega - the theme song was remixed, titled Quartet of Multiple Futures, and included in the 2010 release Hatsune Miku Project DIVA Arcade, complete with vocaloid lyrics.