I have nothing but love for the Guilty Gear series. Word is bond.
However, this may be its compulsory misstep. Every long-running series, no matter what the genre, has to have at least one game in the series that no one wants to talk about. It's the black sheep of the line, the serious misfire; it's the Wand of Gamelon, the Street Fighter: The Movie, the Mortal Kombat: Special Forces.
Guilty Gear Isuka is one of those games.
If you are unfamiliar with Guilty Gear, then this isn't the place to start. Go find a copy of #Reload, play it for a while, then come back.
Isuka is basically Guilty Gear XX#Reload minus Instant Kill moves and the plot, plus four-player simultaneous brawls. Those brawls can be found in the Arcade game, which is a new take on #Reload's Survivor Mode, complete with the character leveling up as he plows through the other characters; Boost mode, which turns the game into Streets of Rage; and, of course, Vs. Mode, which might be the best reason there is to own a PS2 multitap.
On paper, this is kind of cool. If you're working off of screenshots or gameplay movies, Isuka looks great, with plenty of fast-paced, frenetic action, and Daisuke Ishiwatari has contributed another seriously kick-ass soundtrack. That's always been one of the big draws of Guilty Gear: its combination of great music, amazing animation, idiosyncratic character design, and over-the-top action. All of these things are present in Isuka, so the game looks like it'd be another winner.
When you actually get your hands on the damn thing, everything changes.
Sammy's big mistake was to try to place the Guilty Gear cast into Isuka without changing them in any way, shape, or form. This makes half the cast virtually obsolete, since in a pitched four-player brawl, the only characters that're worth a damn are either fast or can use a lot of big screen-clearing moves. Many of the best characters in #Reload, like Potemkin or Baiken, are speed bumps in Isuka, because while you're concentrating on one opponent, the other two are going to take your head off.
Right off the bat, that means that half of Isuka's cast is worthless, and the other half will only win if they abandon the tactics and combos that made them cool in #Reload, and just start spazzing on abusable moves as fast as they can. It's shallow, it depends more on luck than skill, and it's just not much fun.
In one-on-one gameplay, things don't get any less irritating. One of the less sensible changes that Sammy made is to disable characters' ability to automatically turn around, so you have to tap the R1 button to face in the opposite direction. This makes jumping constantly over your opponent's head a viable tactic, since now they can't get any special moves off; since a move's inputs depend on the orientation of your opponent, you can't complete it.
GG Boost would actually be playable if not for the R1 button. It's a cool idea to take fighting-game characters and put them into a beat-'em-up; I'm still convinced that the only reason to play Tekken 4 is the Tekken Force minigame, complete with its idiot bosses. Boost is kind of the same thing, where your character and all his special moves get to take on an army of faceless minions. However, just like playing against the CPU, Boost mode is a constant process of getting punched in the back of the head, because you're always surrounded and saddled with a totally nonintuitive control scheme.
Guilty Gear Isuka could've been great, or at least as good as the weaker fighting games in the series, but it makes the same mistakes that a lot of games have made over the years. If you're going to put characters from one kind of game into another, you need to be willing to make the changes to both controls and capabilities that each character will need in the new genre.
Isuka would've made a great 3D brawler in the tradition of Power Stone, or a cool two-on-two team game like X-Men vs. Street Fighter, but in its current state, it's just not much fun at all.