U.S. market retail tracking firm NPD released its December sales numbers as well as overall 2011 sales.

Retail sales of video games generated revenues of $9.3 billion, which was an 8 percent decline over the $10.1 billion generated in 2010.

"Overall industry results are not entirely surprising given that we are on the back end of the current console lifecycle, combined with the continued digital evolution of gaming," said NPD analyst Anita Frazier. "Core gamers continue to be engaged and spend on established franchises across both the digital and physical format using multiple devices for different gaming occasions."

On the hardware side, Xbox 360 was the best-selling hardware platform for 2011, outselling the second place console by more than 2.7 million units. For December, Microsoft sold 1.7 million consoles in the U.S. As of this time, Nintendo and Sony have not released hardware sales numbers. We'll update this story if they do.

“Hardware was particularly hard hit in December. Normally, we see sales increase from November to December on an average sales per week basis (keeping in mind December is a 5-week retail month as compared to November which is a 4-week retail month)," Frazier added. "The 3DS and the DS were the only platforms to realize a unit sales increase versus November, which is highly unusual since typically all platforms enjoy a lift in the biggest month at retail.”

Below are two lists. One is for overall sales for 2011 and the other is December only.

Annual 2011 Top 10 Games (New Physical Retail only; across all platforms incl. PC)

1. Call of Duty: Modern Warfare 3 (360, PS3, Wii, PC)**
2. Just Dance 3 (Wii, 360, PS3)
3. Elder Scrolls V: Skyrim (360, PS3, PC)**
4. Battlefield 3 (360, PS3, PC)**
5. Madden NFL 12 (360, PS3, Wii, PSP, PS2)**
6. Call of Duty: Black Ops (360, PS3, Wii, NDS, PC)**
7. Batman: Arkham City (360, PS3, PC)**
8. Gears of War 3 (360)**
9. Just Dance 2 (Wii)
10. Assassin's Creed: Revelations (360, PS3, PC)

“Call of Duty:  Modern Warfare 3 landed in the top spot for software title sales for both December and for Annual 2011," said Fraizer. "Looking at the top 10 titles for the year, two franchises scored with two titles each:  Call of Duty and Just Dance – two franchises that couldn’t be more different, demonstrating the range of appealing content on consoles in 2011.”

December 2011 Top 10 Games (New Physical Retail only; across all platforms incl. PC)

1. Call of Duty: Modern Warfare 3 (360, PS3, Wii, PC)**
2. Just Dance 3 (Wii, 360, PS3)
3. Elder Scrolls V: Skyrim (360, PS3, PC)**
4. Mario Kart 7 (3DS)
5. Battlefield 3 (360, PS3, PC)**
6. Madden NFL 12 (360, PS3, Wii, PSP, PS2)**
7. Assassin's Creed: Revelations (360, PS3, PC)
8. NBA 2K12 (360, PS3, Wii, PSP, PS2, PC)
9. Super Mario 3D Land (3DS)
10. Batman: Arkham City (360, PS3, PC)**

**(includes CE, GOTY editions, bundles, etc. but not those bundled with hardware)