The game has not changed mechanically. There are a few minor rules updates, but these would have been done regardless. Other than a few icon updates and the location of some information being moved around to new locations on the cards, both new and previous releases can be mixed and used together. (We recommend sleeves as the backs will be different)
A player can now have up to 3 Reinforcement Gladiators in their Gladiator stack, and no limits as to how many of those three can be brought into play. Also, Reinforcement Gladiator's Maintain costs (if any) are no longer mandatory. There are no mandatory Maintain costs.
Cheer is generated whenever a Gladiator attacks a character, not just an Unset character.
A Protecting or Intercepting character can deal Defense Damage.