Just so you know, that game keeps getting more and more broken as time goes on.
A shame too, it used to be great. I guess it still is to a point. But the end game stuff is . . . broken.
You can power level 70 levels in 30 minutes if you want to.
But most people do it normally and just play.
But every level beyond that 70 mark starts to take multiples of the time you spent to get to 70.
Mythical gear requires lvl 74, and is pretty much a base entry level requirement for Nightmare difficulty; but getting to 74 is the most painful slog i've ever played through, especially if you have multiple characters.
Then there are other loot qualities above mythical, but I've only seen one or two pieces of them in shops. Never dropped during game. And I'll never get to use them, because spending 3 days afk power leveling just to advance half a level isn't fun to me.
I would go back to just insane difficulty, but the gap between nightmare and insane is so inconceivably huge . . .and is the main reason end game is broke. If you can complete atleast one level on nightmare, anything, ANYTHING you do in any lower difficulty is now a certified cake walk; you could only lose if you tried, and even then I've had my pets be able to slaughter everything approaching the crystal. So your only option in your ability to lose is to step away from the crystal and build no towers, and just let it die.