2D fighters have not traditionally made smooth transitions to 3D. Capcom's Street Fighter EX series can't compare to the original SF games, and before the relative success of Deadly Alliance, Midway released the laughable Mortal Kombat 4.
SNK's had mixed success with 3D before now; their biggest advantage is that their worst 3D games are also the hardest ones to find. The Samurai Shodown 64 games are notoriously bad, but they're also Hyper Neo Geo 64 cabinets, which means they are slightly less rare than hen's teeth.
On the other end of the spectrum, Fatal Fury: Wild Ambition was a good arcade game, but most people only know it from Agetec's floaty, murky, nearly-unplayable PSOne port. Since there might've been five FF:WA cabinets in North America, Wild Ambition has a bad reputation that it doesn't deserve.
(A sidenote: if your first experience with any SNK fighting game was on the PSOne, you played a really bad version of the game. Try the versions on the Saturn, Dreamcast, or PS2 instead.)
With King of Fighters: Maximum Impact, SNK takes a fourth stab at 3D action, taking most of the main characters from the KOF series--Terry Bogard, Kyo Kusanagi, Iori Yagami, Mai Shiranui, Ryo Sakazaki, a few others--and dropping them into the middle of a gang war.
The new King of Fighters tournament is being held by the Metatron Foundation, the public face of the shadowy crime syndicate Mephistopheles. (Overt and somewhat botched Judaic symbolism: check.) This year, the tournament is set in Southtown, with the winner getting to take on Mephistopheles's leader Duke.
If you want any more storyline than that, you'll have to play as the new main characters: Alba Meira, his brother Soiree the gay rodeo clown (I don't mean that as a perjorative, I mean he really is a gay rodeo clown), or Lien Neville, an English assassin who is attending the tournament for the purpose of challenging Mai to some kind of cleavage duel.
You could also play as Mingnon Beart, but she's an affront to all things good and true. Let's all ignore her and hope she goes away.
Oddly for a KOF game, Maximum Impact is a one-on-one tournament fighter with no team options to speak of. It uses the typical best of three format, as well as a three-level super meter like those found in KOF. Several super moves will require more than one level of meter to pull off, but meter's very easy to come by in MI; you get a level for landing the first attack, which means if you open with a super, it might've been free.
The gameplay itself is a little weird. SNK's done something unique here, in that they've tried to make a 3D version of a 2D game that's exactly that. It's not Street Fighter EX, which was really a whole new game with vaguely familiar characters; it's KOF translated into 3D, right down to several moves making the transition intact.
Maximum Impact is a lot looser and faster than your average KOF game, and fireball wars are a thing of the past, but it genuinely feels like a 2D KOF, right down to the nearly unbeatable final boss. (Duke's not the greatest fighter in the world, but he's got an infinite supply of meter and a super move that's completely invincible at startup, does 50% damage, and will probably guard crush you. Nice one, SNK.)
The character models are serviceable. If you've played Bloody Roar 4, Maximum Impact looks about as good as that did. It's not spectacular, but the frame rate never drops and everything's recognizable, which is good enough for me. The real problems all arise from some dodgy character design, like Mingnon's gravity-defying Princess-Leia-sideways hair.
...wait, we're supposed to be ignoring Mingnon. Never mind that. I never said it.
Most of the really impressive graphics in Maximum Impact come from the backgrounds, some of which look really good. Unfortunately, nowhere near as much effort was put into the game's sound. The music's not among SNK's best work, while the voice acting runs the gamut from decent (Chae Lim, Clark) to jaw-grindingly horrible (Athena, Kyo, She Who Must Not Be Named).
That, at least, is sort of in keeping with KOF tradition, as a lot of the dialogue and sound bites were translated literally from the Japanese by a hard-working team of howler monkeys. To hear Mai speak in Maximum Impact is to know true hilarity. ("Folding fan! Super... deadlyninjabees! Yes, Japan's best!")
Like Mai, each returning character has access to their usual techniques, and they've translated most of them into English for your convenience. (I'd really rather they hadn't. Shouting out attack names is cool in Japanese, but usually sounds stupid in English, and I'm not sure why.) They've also all got a few new command moves, but other than that, even some of their normal punches and kicks made the transition intact.
One concern I had when I first heard of Maximum Impact was that SNK was going to plug characters into the new engine without making sure they'd actually be playable first. (You know how Zangief's completely unplayable in Marvel vs. Capcom 2? Same thing.)
Fortunately, that isn't really the case. Everyone in Maximum Impact is at least playable, although some characters run away with the game, like Soiree, Kyo, K', and Alba. A lot of the time, what separates a good character from a bad one in Maximum Impact is how badly they can bludgeon somebody who's lying down.
That, combined with some truly ridiculous combos that either aren't possible or haven't been possible for years in the core KOF series (like Athena standing over a prone opponent and activating her Crystal Bit), can make Maximum Impact a chore.
As a KOF game, Maximum Impact is pretty shallow, while as a 3D fighter, it's a bit of a throwback. It's also got a really cheap final boss, a couple of unavoidable balance issues, and the Challenge Mode can be insanely difficult.
If SNK can iron out the flaws in its engine and its character balance in time for Maximum Impact 2 (which is in development as I type this), then this'll be a series to watch. The game as it stands, however, is initially fun, but it wears out its welcome pretty quickly.