I'm just saying that if you are truly personally invested in this game and it's characters (John especially), you'd be interested by this expantion and revelation of identity and moral. I can see where you don't think it was a viable 'cliff-hanger' Legendary ending, but by the same token it does it's part to build just as much anticipation for Halo 5 as Halo 3's ending did.
Again, I'm pointing out that through showing his eyes, and everything else in H4's story, it's bringing forth this new, or better put, less emphasized perception of an old and loved hero.
Further, it's letting us know that the Chief is embarking on a new journey, and new chapter and it's one he's beginning without Cortana, and without his stoic and invulnerable security blanket of a persona.
Personally I find the Legendary ending here did more than intrigue me as to what to expect for 5, but I understand to each their own, and I see what your saying. Just try to see what I'm saying too!
And that's what I was going to say, I'm sure by the end of Spartan OPS, you'll receive your broad and extravagent what's-next ending, even though it's not through the Campaign directly.
I just found this more subtle and personal nod at what to expect, and what's happening with Chief - with John, to be more powerful and altogether more exciting.