The problem is that there's a number and a subtitle. "Halo 5" would sound fine, so would "Halo: Guardians." Having both makes me think of Halo 3: Recon or something.
Unless that's the point, and there's gonna be a Ground Zeroes type thing happening.
I think it's what happens when 30 people try to combine the marketing of Star Wars and Call of Duty...
Guardians have been part of Halo lore since Halo 3. Bungie's fault for reusing the name.
Guardians of the Mantle!!! yes. not Guardians. without the Mantle, guardians has no place when you have stories about Spartans. and bungie strayed far away from Spartan whereas it's a common thing too when talking about soldiers.
And when has the baton between Forerunners and Humans passed? do you think many people will get "it" after Halo 4 story handling?
no...you will need to read a carefull crafted book that will impy but not tell too much etc...
and what is the Mantle? it's dead "thing" as of now. So implying it's existence with the subtitle while featuring Spartans...is not great.
So far the Guardians of The Mantle are the Forerunners. The rest is just implied. and the Mantle having not manifested yet to any human...
If you feel happy about the reveal, I'm very fine with it. I'd like to be you right now.