It received almost no publicity and was more or less completely ignored both inside and outside Japan. Very few copies of either the Playstation or arcade version were produced, and you can easily go weeks or months without seeing a copy come up for sale online or off.
The basic gameplay is instantly recognizable: Coloured things fall, and you match 'em up. Easy, right? Match up four or more of the same colour and they disappear. If the remaining balls fall into a position where four more match up, you get a combo, and combos are used abuse your opposition with shielded balls. These shielded balls must first be next to a matched set before they can be matched themselves. While it sounds like the same puzzle game you've played before, one unique twist really sets it apart: the triplets are not glued together once they land, and the balls will tumble down the pile. It takes a few plays to get used to how they roll, and plan your moves accordingly, but once you do everything changes. It's very hard to go back to a static falling-block puzzler like PuyoPuyo or Tetris after the strangely fluid dynamics of Battle Balls.
The usual game types are here: 1P solo, 1P vs CPU, and 2 player VS. The graphics are solid but not exceptional, and include all the different backgrounds, character animations and flashy-but-not-too-flashy effects you'd expect from this genre. The music is a shining star, and is - to put it mildly - exceptional. Few games can claim to have music as suitable as this, and only Taito's Puzzle Bobble (Bust a Move) springs to mind as a comparable soundtrack.
Released only for the Playstation and Seibu's own SPI arcade system, the game is quite rare. It still doesn't have any name recognition or demand, which is a bit distressing. No one I've introduced the game to fails to adore it and covet their own copy. No one who has one will part with it. There was a demo of this on the Raiden DX release for Playstation, but DX is itself rare and this demo serves only to introduce it to a very small number of people.
Battle Balls is simply exceptional. There's no part of the game that isn't honed to perfection. It introduces a nifty twist to the puzzle-game genre, with oodles of polish, and it's an absolute shame this game wasn't more well known.
(This was originally written in 2003)