For the second week in a row, Nintendo's new 3DS handled has been outsold in Japan by Sony's PSP, a device originally released in 2004. Sony sold 35,000 PSPs from April 4 to 10, topping the 32,000 3DS units sold.

Lukewarm sales of the 3DS since its  Feb. 26 release in Japan have fueled speculation that Nintendo's latest handheld may fail to see the success enjoyed by its predecessor.

In Japan, launch sales for the 3DS topped 400,000 within first two days, roughly the same number sold during the week following the console's release in the U.S. While striking, those numbers aren't at all surprising, and follow similar trends set by sales of the Nintendo DS. The original DS saw sales of 480,000 following its Nov. 2005 release in the U.S, and the DSi moved 435,000 units upon its release in March 2009. But the 3DS' strong launch was followed by a nosedive in sales big enough for the PSP to overtake it.

The reasons for this lie largely in software. As evidenced by the recent spike in PSP sales, software is a major driver of hardware sales in Japan, not the other way around. Earlier this month, sales for the PSP rose on the release of Amagami, a dating simulator originally released for the PS2 in 2008. That trend continued last week with the release of Earth Defense Force 2 Portable, which topped Japanese charts at 63,795 units sold.

So far, software is where the 3DS has faltered most. Sixteen games were released with the 3DS in the U.S. in a line-up that included three titles from Nintendo itself. Quantity, however, was not matched by quality. The average Metacritic score for the 3DS's launch line up was 69, a number that confirms why so many gamers have been unenthused by what the 3DS has had to offer.

Super Street Fighter IV: 3D Edition has been a notable exception to that. With an average Metacritic score of 85, the title is the best-reviewed game currently available for the 3DS. It is also the best-selling. Capcom confirmed last week that it had shipped 1 million copies of the game worldwide since its release.

If that pattern holds true, the next few months are when sales of the 3DS will likely pick up, as a number of significant new releases make their way to the console. In June The Legend of Zelda: Ocarina of Time 3D will reach the U.S, Japan, and Europe. The title will be the first significant release from Nintendo outside of the 3DS's launch window. Another major title, Resident Evil: The Mercenaries is also slated for a June release in Japan. It is likely that the release of these titles, as well as Koei's Dead or Alive: Dimensions, will mark a shift in the 3DS's software lineup to more critically-successful titles.