It turns it into something like Hotline Miami, where there's a room full of guys who can kill you almost immediately, so you wind up playing the encounter over and over until you have the perfect path of devastation through the enemies.
The main thing I disliked about Eternal was the added story elements, the very minimal story in 2016 was so perfect (it's basically: you wake up, you're badass, you hate demons, go rip and tear). Eternal tried to go for some sort of Doomslayer lore - spelling it out makes it lame.
Overall, both games are great, and I very much enjoyed them.