Endless Space 2: Harmonic Memories

While not drastic pieces of content, for their price, Celestial Worlds and Harmonic Memories add a valuable boost of replayability, the best friend of any strategy player. I would especially recommend both DLCs for any player who has yet to play one of the Endless Space 2 races, as the new quest-line, music, unique planets and improvements add a slightly richer campaign experience on the whole.