This is the big boss you see in every promotion for Doom 2016 when it was set to launch. The demon that rips open the obligatory video game elevator you were just about to take to the next level to say "Hahaha, yeah no, you ain't done, get the hell back out here," and proceeds to fling you out to beat you into putty.
Naturally, such an insult cannot stand.
This boss fight is pretty much everything you've been going through up to this point, but against a demon who actually takes a few more punches than usual to go down. Which is perfectly fine with us, given that Doom 2016 is one of the best games of the decade, so more of the same, but with a larger boss, is just fine, thank you.
But more than that, it's challenging without being crushing, the boss fight moves at a steady pace, and when you take it down, you feel like the top dog, and that feeling is earned. Sometimes simplicity is best, and this is the boss fight that exemplifies that.