Cracked.com's Jason Iannone, on the game-changing nature of AGI versus its portrayal in fiction:

Cortana, the Chief's AI sidekick [in Halo] [...] can control entire cities by remotely breaking into their battle nets and taking over their weaponry, without anyone ever setting foot in the area. Which is another way of saying that she really doesn't need the Chief at all.

[...] Master Chief, for all his badassitude, is really just a grunt whose life is being put unnecessarily at risk, although a video game featuring him doing nothing but sitting around eating tacos in the cafeteria while Cortana does all the work would probably not have sold as well.

From 6 Video Game Heroes Made Useless By Supporting Characters. High Challenge is relevant to the closing point.