Ok let me clarify, now that I'm awake and not using my iphone.
Halo 4 biggest and best sales out of the box. But, with that said people still keep using the faulty comparison of comparing Halo's start to the total lifetime sales of Halo 3 and Halo Reach that have both been sold on retail 6 years and 2.5 years respectively.
Post Call of duty era, no other shooter exclusive period does the numbers Halo 4 has done, let alone no other exclusive has performed like Halo 4 since Reach. In fact, nothing in 2013 is going to perform at that level as well.
On Xbox Live activity, like Reach or any other Halo, H4 will be a staple on live until the next Halo arrives. The Activity list doesnt mean theres more of a consistant population whose playing on over Live that the other. The only time you can make that distinction on Xbox Live is if you compare two shooters for that given week on Major Nelson's List.
It's clear that there are other factors, when you have a game like Minecraft where people I know stay on there for hours and hours every day as opposed to a thousands and thousands of users per hour playing a few matchmaking games.
If this wasn't the case you wouldn't see games like Skyrim and Bioshock: Infinite hugging the Xbox Live Activity top 10 on a given week.
At the end of the day, H4 was an outright success, like any game, especially on forums it's going to get bagged on by it's detractors, but if you apply the same logic to the competitors then that means MS is in the drivers seat with the Halo IP going into next gen. Because, if Halo 4 numbers means your franchise is dead, then the competitors software must be comatose, by those same standards.