The rules are as simple as we can make them. Gladiators fight endlessly, gaining standard levels of XP and GP, in a race to level 20. The most unusual feature is that it does not work in rounds - people fight whenever they have an opponent that is ready.The Arena of Blood is a place beyond time and space. Beings beyond comprehension pit gladiators of all kinds against one another, eternally restoring them to fight again.
The reason, and I'm not defending this concept in any way, is that it's a lot of fun. What builds work? Is it rock-paper-scissors, or is there a strategy that beats all? Do you know your rules well enough to fight flawlessly? Frustrating or fabulous, it's always time to try again.