DEATHSMILES! The game sold 20,000 copies in Japan during its first week on sale. This is the first traditional shooter to break the Japanese top ten this generation.
Originally an arcade game developed by Cave, DEATHSMILES was the company first effort at self-porting and self-publishing an Xbox 360 title. Previously, Cave had brought in developer 5pb to handle the porting duties.
The second highest shooter debut for this generation is Konami's Otomoedius G, which sold 15,000 copies in its first week. Check out the DEATHSMILES trailer here. It's fantastic.