In Halo 4 on the Xbox 360, there is an alternate ending that you can see, which actually unveils Master Chief for the first time in any Halo game to date.
I won’t spoil anything else for you, but I’m pretty sure long time Halo fans are going to enjoy this one.
Seeing the alternate endings doesn’t take a bunch of online crap like Mass Effect 3 did (sorry BioWare, but that was kinda lame).
All you need to do to see the alternate ending to Halo 4 is to beat the game on Legendary difficulty.
This can sound kind of daunting for you casual gamers, so I suggest getting some friends and going through it in co-op. It’s a lot more fun that way, and every Halo game I’ve played to date has been easier to beat on Legendary with more people helping out.