The game brings reworked 4K visuals. Furthermore, players will get to play a new campaign titled “The Last Khans” along with remastered audio, a new AI (the best AI ever in an Age of Empires game, which can compete like a professional player without cheating) and more of 200 hours worth of content with the single player campaigns alone.
https://www.pcgamer.com/age-of-empires-2-definitive-edition-confirmed-at-e3-coming-this-fall/
https://www.pcgamer.com/age-of-empires-2-definitive-edition-confirmed-at-e3-coming-this-fall/