Halo 2
Nov 9th 2004 - April 17th, 2007
Halo 3
Sept 25th, 2007 - Feb 2nd, 2010
Halo Reach
Sept 14th, 2010 - Nov 15th 2011
Halo 4
Nov 6, 2012 - August 20, 2013
The earlier games stretched DLC out for years. In Halo 4, we have all the DLC before the game's first anniversary! (Personally, I feel this was actually planned by the greater Microsoft peeps to help move users to the Xbox One away from games on the 360.)
I think it's obvious that there's not as many players playing Halo 4 as previous Halo titles, but I think your well-known opinion of the game is helping you ignore other outside influences on sustained video game players. As compared to even as short of a time ago as Halo 3, you have a proliferation of on-demand everything, smart phones, tablets and Movies/TV/Netflix on video game consoles.
Plain and simple, by the numbers that matter to Microsoft ($$$), Halo 4 was successful. That's a good thing. It's just a GREAT thing that 343I seems to acknowledge the shortcomings of their still really good, first ever video game as a company. Halo 4 may not measure up to the "Avateur Scale of Success™", but I and many others enjoyed Halo 4. I'd say a lot also seem encouraged that Halo 5 will be an even better game than it's predecessor, and that's exciting.
- MacGyver10