I'm confused cruel is hardcore or?

Wait until Merciless and you get an automatic -60% all resists and lose 10% experience when you die.

standard, hardcore, ambush, and invasion are leagues (servers) with different rules. Most players are currently playing on ambush and invasion. standard and ambush are softcore leagues, invasion and hardcore are hardcore leagues. when a character dies on a hardcore league their character is transfered to standard.

Normal, Cruel, and Merciless are difficulty levels within the game, the same on all servers. Basically, in the course of leveling from 1-100 you will play through the story campaign 3 times. It gets progressively harder each time, via resistance penalties and experience loss on death.