Bangai-O Spirits shines because it's not easily classified as any given kind of game.
At this point, it is almost cliché to refer to developer Treasure as "quirky". Clearly they've got their own design aesthetics. What is most impressive about Treasure, however, is that their vision tends to come through in both original properties (where they certainly have the most creative control) and licensed material (where they presumably do not). It is almost always the case that a Treasure-developed game will bring its own frenetic sense of style to the table, and this is particularly true in the case of shooters. Arguably, the Treasure stable of shooters is what has led to their status as a cult developer, and as such, each new one is met with a good deal of anticipation from studio fans.
Bangai-O Spirits is no exception, and despite the fact that it is a sequel to an N64 (and later Dreamcast) title, it is extraordinarily unique. Where Astro Boy: The Omega Factor impressed with its adapting of a licensed property to the Treasure style, and Ikaruga became a cult classic on the strength of its brilliant polarity mechanic, Bangai-O Spirits shines because it's not easily classified as any given kind of game. The player pilots a mech and has a variety of weapons with which to customize it. But the mech is piloted in eight directions on a two-dimensional plane, and the action is zoomed out enough that at a casual glance, it might seem simply to be a traditional shooter. At the same time the level designs, at a core level, lend the title an extremely puzzle-oriented quality. This blending of styles is at once risky and rewarding.
Traversing any given level, and defeating the enemies within, typically requires careful consideration of which weapons to equip your mech with beforehand, along with a healthy (though not frustrating) dose of trial-and-error. Combination bonuses between normal and special weapons in certain configurations complicate matters further. Is variety or power more valued in your arsenal? The answer to this question will rely as much on the player's particular style as it will on the level itself. There are levels which can be construed as mazes, boss battles, bullet hell shooters, and everything in between.
Interestingly, the credits actually roll once the tutorial sequence of levels is complete. Although the game does come packed with a copious number of other levels, what is really presented here is a game framework. The level editor is robust, and hence much of the life of the game can be breathed in via user-created content. The fundamentals of Bangai-O Spirits are strong enough that it will hopefully generate a solid following. Such a fanbase will be critical to its long-term success, though given Treasure's pedigree and its status as a cult favorite developer, it is not difficult to imagine that such longevity is possible.
This is all made possible by Bangai-O Spirits' brilliantly retro and creative mechanism for level distribution, namely sound. By encoding level data as a sound that can be recorded and then input to another DS through the integrated microphone, level swapping requires neither downloading large amounts of data directly to the DS, nor entering lengthy codes via the touchscreen. Perhaps more notably, this method of level sharing completely bypasses the need to interact with Nintendo's frustratingly restrictive friend codes.
An already solid package as it stands, Spirits has the potential to experience a good deal of longevity due to its level creation and distribution framework. Further, it functions equally well as an introduction to Treasure neophytes and as another potential cult favorite for long-time studio fans. It is easy to imagine that Spirits will not be a commercial success given both the relative dearth of promotion behind it and its nature as "another quirky game from Treasure", but hopefully word of mouth will gain Bangai-O Spirits the attention it rightfully deserves.