I was looking at the original year of the Xbox 360s release from 2005 to 2006 to see what happened when the console was 'without competition' and two areas came to my attention.

The first coincided with March 2006. This was the release of Oblivion, before that the Xbox 360 was trending down to around 55-60K a week and after the release of Oblivion there was a noticeable spike of sales increasing week after week peaking at 134k several weeks later. Its quite possible that the release of Oblivion lead directly or partly to the sale of at least a third of a million (333k) Xbox 360s during the following 6 months of sustained higher sales. 

The second coincided with November 2006 and the release of Gears of War. 6 million sales are a testament to the impact that this game had on the early part of the generation. It seems probabe that the momentum of the Xbox 360, especially in the U.S. reached critical mass at the point of release of this title. This title most likely sold a million consoles for Microsoft in the months after release. This title is probably the number one system seller on HD consoles this generation. The reason? It was an unexpected addition to the lineup, not something people purchased consoles for and planned from the start. It tapped a virgin audience of 'swing voters'.

The two titles, Oblivion and Gears of War, in my belief created the Xbox 360 we have today. The first carried the Xbox 360 through the lean time of its first 6 months of release and the latter which is probably the premiere system seller on HD consoles to date saw the console through the release of the PS3 with strength and momentum. So whilst the release of Halo 3 in September 2007 sealed the deal, these two titles made the play that got the system this far. 50% more sales than the previous Xbox and at a 50%  higher average sale price is nothing to sneeze at.

Check out the graph for yourself: http://vgchartz.com/hwcomps.php?cons1=Wii&reg1=------&cons2=PS3&reg2=All&cons3=X360&reg3=All&start=38662&end=39145

March 2006 also coincides when MS was able to have production catch up with demand. The Worldwide launch kept 360s in very short supply until early spring 2006.

Yep yep , the only reason i got a 360 was For Oblivion and Gears of war , and it turned out pretty great.

i'd have said the halo/gears/live combo did it.

I agree. I got my console for Oblivion and later Gears of War was the first game to blow me away this gen and really turn me on to multiplayer.

Oblivion is definitely worth buying a console for in my book.

2 great reasons to have picked up a 360 at the time.

I still remember walking by a crowd standing around a TV in the mall watching a kid play Gears at the gaming store. Withing a few minutes of watching the game, several walked out with 360's. Gears was a massive console graphical step up at the time of release and is still one amazing looking title.

Not really, we all know that without the Halo Franchise, the Xbox will sell even less than the PS3, which is a good thing if it did =)

I noticed the same, I didn't notice anyone buying any Xbox 360s though.