A common misconception about the greater rifts once you venture into the madness of 35+, is that you're often at the mercy of crazy randomness in form of extremely hard mobs, empty levels and just general tomfoolery that you never see in normal games.
I'm here to let you in on a secret ...
THERE IS NO RANDOMNESS INVOLVED!
The way this works is that Blizzard has actually employed Diablo himself sitting there, carefully crafting these maps and putting the mobs in that will annoy you the most, and generally just doing everything to fuck you over.
A few examples! After dying excessively at GR 37 due to the "jailer oneshot", I decided to change my amulet to lower my DPS slightly, but become immune to arcane damage. At this point I had 4 GR37 keystones ready to go and I set out to slaughter enemies. Now, if there had been randomness involved, I would've CERTAINLY faced AT LEAST ONE FUCKING JAILER MOB in those 4 runs, but alas, no such mobs were seen. The icing on the cake was how the boss in the last of the instances, once the timer had expired of course, decided to send out a plethora of arcane sentries just to mock me.
Obviously I would have none of this tomfoolery, switched my neck back and set out to annihilate. On the first map of doing this, I encountered 9 elite packs, 4 of which had jailer. I shit you not. This can't be random!
Another observation involves the mob density and elite compositions! I ran a few rifts where the amount of elite mobs was ... well, not enough to have a >50% uptime on Bane of the Powerful (rank ~35), which just doesn't make any sense! I did some quick math and decided to give another gem a try. Sure enough, I enter the next rift and I'm greeted by no less than 3 packs of elites within shooting range of the entrance. Random? I THINK NOT!
The worst examples are when whoever sets up the games tends to be sadistic. They leave you with a glimmer of hope, which fills your heart with confidence, before taking it all away in an instant.
At one point I was running around gleefully as I was ahead of the timer, slightly concerned about mob density and how it was probably the longest map I could remember running, but, I was focused! At 90% progress, I open the door forward and everything crumbles. There's one yellow and one pack of blues in the room, now, I shit you not, both of them are ghosts - essentially the homing search and destroy mob in Diablo 3, running through walls - no problem! The yellow was obviously Horde, and all his minions were FAST, which essentially implied that I was about to be swarmed by a throng of twoshotters all cranked up on speed, who didn't believe in obstacles such as SOLID FUCKING WALLS when it came to chasing down their target. The blue had probably my favorite combination in the whole world at Greater Rift 35+ Jailer, Frozen and Thunderstorm! Needless to say, I had quite a few 1m30s runs to get back to where I died ... repeatedly.
So, don't blame randomness if you can't beat that greater rift which is just apeshit retarded, it's clearly too much bullshit to be random, blame whoever is sitting there generating these maps of pure evil JUST FOR YOU!
Also, I hope whoever made the Cesspools map combined with whoever did QA for said map is forced to only ever play that over and over and over again. The freezes combined with the fact that you don't get a CHECKPOINT ups the population of frowntown by at least one every time.
*sigh*
But it's too much fun! :(