First off: Would I recommend this game? Yes and no.
First thing to consider is that this is a rather old PC port of a spinoff 'experimental' title of the main Guilty Gear XX series. It's unfortunate that the more traditional Guilty Gear XX #Reload wasn't placed on steam, however, the publisher of that title for the PC either no longer exists or is not interested in selling it here. Secondly, as it's a fighting game, Guilty Gear Isuka pretty much relies entirely on a controller to play the game to any reasonable extent that it is actually fun. That isn't a problem for myself, but for many people who are 'hardcore' PC gamers and lack a compatible device, that can be a dealbreaker. Third, as mentioned earlier, this game is very 'experimental' and as a result isn't nearly as polished as much of the other games in the series.
However, despite all these flaws, the game can still be very enjoyable, and in some ways, more enjoyable than the main series (in certain situations).
Guilty Gear is a series that is famous for it's intense speed, strange characters, and technical complexity. That last one is the reason a controller is necessary; the inputs required to perform even basic combos is just way too clunky on a keyboard. Whereas slower fighting games can be casually played on a keyboard if you're really hard up for cash, Guilty Gear is simply too fast paced and complex to do without a controller. In fact, an arcade stick is suggested for most players. While the series briefly pops into the general spotlight once in a while when a new title is released, it often fades out of the public eye for the most part soon afterwards. Despite this habit of people seemingly forgetting this series existence, there is a thriving community of players from all around the world-- surprisingly one of the most stable and best gaming communities I've ever been a part of. The community is driven by competition. Guilty Gear may be famous for it's quirkiness and speed, but in the fighting game community, what really sets it apart is how amazingly well balanced the game is. Every character can win, with enough skill; Tier listings are merely a suggestion of relative strength of a character based on how often that character wins tournaments, not whether a character is overpowered or too weak to compete; Strong system mechanics tie together interesting character mechanics into a cohesive battle system that is both intuitive and deep; And if you enjoy the game, putting in the time to get better becomes infinitely more rewarding and fun.
This is all true of nearly every Guilty Gear game, particularly the ones starting from #Reload and after. This does include Isuka, but with a grain of salt.
For Isuka, the developers attempted an idea that hadn't really be executed in a 2D fighter before: 4 player simultaneous combat. In 3D fighters this has been done many times, and there have been tag team games for ages, but this was the first time in a 2D fighter where 4 players could simultaneous duke it out. Unfortunately, these characters are carbon copies of their #Reload versions (with the exception of the first appearance of A.B.A.) and therefore were not designed to play in a 4 player environment like this. The only appreciable difference between the versions of the characters is that they have additional attacks and animations to change 'lanes' on the stage to determine who they want to attack. These attacks aren't exactly good or efficient to any extent, making them pretty useless in actual gameplay. In fact, the addition of a background lane was poorly executed itself, as seeing what's happening behind the foreground players is difficult due to the style of animation used, which executes a lot of special effects and can cover a great deal of the screen.
This isn't to say the game isn't without it's merits, however. This game makes a great party game; however, lack of internet play means you're gonna have to find some buddies to hang out and play on your PC with. The game is quite old now, however, so theoretically it should run on most laptops without much of an issue, so it's pretty portable in that respect. Free for alls can be hilarious and silly (especially if everyone chooses Potemkin), and 2v2's can be intense and produce surprisingly awesome combos and mixups. 1v1 feels wonky because the addition of the background lane and the turn button is clunky when there's only one person to focus on; it's unfortunate that a regular 1v1 mode like #Reload was not included. Another addition was the Robo Ky Mk. II, which is a second edition of Robo Ky that is highly customizable, allowing you to equip practically any special move that any character in the game possesses. The animations for this are often hilarious and absurd, such as pulling out a gigant electrified fly swatter for Anji's command grab attack, or a giant frying pan for Zappa's Raou Bellow's Malice super, and flinging bacon at the enemy. You could level up and earn points to purchase these moves and stat bonuses from the games 'GG Mode', which is essentially an adaptation of the normal system inside a beat'em up like stage. The better you perform (higher damage/longer combos, not getting hit, etc.) grant more points and even unlock special things like Kakusei Sol and Kakusei Ky, which are incredibly broken and fun characters. The enemies for the GG Mode are not full characters at all-- most have a total of three attacks, however, they too are unlockable. For the arcade mode-- which is probably incorrectly named, considering it's much more like a survival mode, you can play through 50 levels at a time of increasingly difficult battles. You can play with a friend or alone, and every 50 levels you can increase to the next 50 levels, which culminates at 1000 levels of gameplay. This may sound like a walk in the park, however, the opponents get incredibly difficult, and the final boss for every 50 levels is a 'Gear' named Leopaldon. He's big, mean, and has super armor and autoblocks, making him quite difficult to beat. Unlocking Kakusei Sol and Kakusei Ky are very difficult but eventually become your best bet for combatting the level 1000 monster of a boss.
The game suffers from a lack of foresight, however. Several characters fail to function properly (Zappa and his Dog summon, Eddie and Little Eddie-- the summons only attack in the direction the main character is attacking, which severely limits the functionality they presented in #Reload. e), and you sort of have to trick the button configuration to set the Dust and Turn buttons to single button inputs instead of multiple button presses-- which there are multiple of in Guilty Gear anyways. The attacks for the characters weren't modified to better suit fighting multiple opponents, even when it seems appropriate, and attacking teammates makes them 'get hurt', although they take no damage, but can easily lead to them taking damage from opponents. This is likely why they added a background lane for the second pair of characters, but it's a lazy solution that could have been avoided by thinking a little harder about the concept. As a result, the game can be... frustrating, at times. Moreso than simply losing in a normal fighting game, because you may lose because your character simply doesn't function properly, or because your teammate hit you. It's an unfortunate departure from the usual level of quality we often see for Guilty Gear (and indeed, any games from Arc System Works in general).
This is all well and good, but is the game fun? Is it worth your money? Potentially. If you're looking for something you can play with your friends, or to see if you might enjoy the Guilty Gear series, this isn't a terrible option-- not the best, but it's not completely awful either. Maybe buy it to see if you like the style and playstyle, then buy one of the other games (Preferrably Guilty Gear XX Accent Core + on ps3 or xbox 360, or Guilty Gear XRD coming 2014). Cheers!