I don't think anyone here said Halo declines because it's old. I said the decline is easy to understand, many factors change during that timeframe and different devs, bad launch of the MCC, strong competition on FPS market, multiplat gamers moving to PS4 for example all have an effect. I've also not used install base as an excuse, because I'm happy to see millions of people bought X1 for other good reasons than Halo :)

But I can't agree with you that it's Halos quality that has declined. I think the opposite as I never liked Bungies Halo much, but I find 343is take on Halo very refresing and high quality, from gameplay perspective. Online experience is superb. And it's also getting good reviews. That said, they probably failed to keep original fans satisfied enough and failed to bring in enough new fans to maintain sales. Then again like a said, it's just a first-person shooter among others so I'm not sure if it was even possible to make enough new fans along the way to maintain its insane popularity.  But who knows, maybe you're right, 343i made a good fps-shooter but not good Halo and all the blame goes to them.

Hey it's nice to see you brought up Gears of War, my favourite franchise :P To quote you "I bet when Gears releases and doesn't do as well as prior Gears, nobody will flinch to say Black Tusk (or The Coalition. Whatever they're going by) < Epic Games."

Sure some would say that but they wouldn't know what they're talking about. Epic Games tanked GoW with Judgment themselves. Since GoW2 there's been constant complaining about Epic and the direction where they took the franchise. Fanbase is divided between original fans and fans of GoW3 and instead making Judgment compelling to both sides or one of them, they made a game that wasn't compelling to either :) 

That puts The Coalition in a sweet but challenging position I think, but that's a whole other topic.