Halo is a massive gaming franchise created by Bungie 

However Halo for me isn't as powerful a brand as it used to be , first there was Halo 4 , then The MCC issues , and now Halo 5 , don't get me wrong it looks and plays amazing but you can't deny it the pace , speed and some features added feel like Titanfall and COD , and you know what thats not a bad thing , the FPS market has changed people need faster paced games , or at least that what the market wants , Halo's problem is that it no longer a genre defining leader of fps on consoles , when Halo games at least from 1 to 3 landed they felt fresh and innovative , thats gone now , and people have started moving to other fps franchises. Halo is no longer the premier title of xbox , it is among 1st party but in general i feel the winds have shifted and Halo isn't as primary a motivator as before in getting an XBox

Personally I feel halo 5 will sell and do amazingly well but I can't see it cracking 6.5million sales Life to date , it could as it's halo but i think the market and times and change 

( i know this necro bump material of the year )

Halo 5 will sell 10 million units.

It will sale fine, did what 8m on a 20m user base.

Time is undefeated my friend. I too am a Halo vet and like you, I too have had to deal with the fact that it's time has come and gone. Halo 5 will come and go, and people will buy it in smaller numbers, but it will never feel the way you want it to, nor have the impact it once had. 

Hopefully, something comes along that can takes it's place for us who like that style of play. If not, I guess we'll just have to adapt.

Halo 5 is going to be huge. Cant wait to see the single player.

I just recently played Halo 1 and Halo 2 on an original Xbox and I was amazed with how good it plays. I'll get a X360 to play the more modern games.

It's not what it used to be, but I like where they are going, at least as far as multiplayer is concerned. Halo 5 beta has been surprisingly enjoyable. I am liking the smoothness and pacing so far.

So what's Xbox's premier exclusive?

I agree that the franchise isn't as big as it once was (although the sales of Halo 4 actually suggest otherwise). But for me, the game itself has found the magic of the first game in the fourth installment and is a better game than ever imo.

It will never ever be as bad as Halo: Reach, so I'm confident that Halo 5 will be, at least, great; and it will perform great in sales too.