Yes, I have the Dungeon Master's Guide....and this book lives up to and maybe even exceeds the expectations set by the prior two tomes in the 5E family. It may be my favorite DMG yet, actually. There's a lot of content in here.
The gritty realism rules option for resting caught my attention and I had to share it, because it's so elegantly simple: under the gritty realism rules a short rest is defined at 8 hours, and a long rest is defined as one week.
So that action surge you want to recover, or that bonus spell slot you need a short rest to regain? Check back in 8 hours. That sucking chest wound you took that won't heal because the barbed devil ate the cleric? Should be fine in a week or so, if you live that long.
Think about that for a moment, and tell me that wouldn't grit the hell out of your game. There'd be so much frikkin' grit you'd need a sturdy toothpick for your teeth. Assuming you had any, in such a gritty world.
I am very interested in trying out a 5E game where the gritty rest rules are on now, it sounds excruciatingly tough. The Dark Souls variant of D&D, if you will.