I think there are two ways to look at Electroplankton; from a consumer standpoint and an artistic standpoint.
From the perspective of someone paying money for this card, I think I would be more than a little disappointed. There are no goals in the traditional sense; no real progression. The average person buys a piece of interactive software and expects certain things, among them the kinds of structure and experience that are usually conveyed by the art on the cover of the box. Jumping. Fighting. Shooting. Electroplankton has none of these things, and eschews all notions of conventional design. If I only had enough money to buy one game for the next month and I had chosen Electroplankton, I wouldn't be happy.
But there's another perspective, as I mentioned—the artistic. Removing any concerns of financial investment, Electroplankton takes on a whole new identity. The visuals are abstract and minimalist, a perfect reflection of its aural persona. By interacting with the simple organisms swimming in digital water, it's possible to create a multi-sensory display of sight and sound unlike anything else. In certain modes, it can be a calming meditation. In others, it's a high-energy activity that makes me want to move.
Much like David suggested in his review, if Electroplankton was in a museum or gallery, it would undoubtedly be heralded as interactive art. Because it uses the DS as its performance space and appeals to one person at a time rather than to a stream of passersby from atop a pedestal, does that make it any less legitimate? I would say not. However, the fact remains that what people expect of art and what people expect of games are two wildly different things.
It's a shame that Nintendo was not able to include a free copy of Electroplankton with every DS, or at least make it more widely available for a nominal fee. It's simply not a game, but it is an extremely interesting and unique experience that might help open people's eyes to the world of possibilities that videogames and the electronic medium have opened.