Terraforming Mars: Prelude is not just the best Terraforming Mars expansion — it is essential enough that I consider it part of the base game. The four prelude cards given at game start allow each player to immediately establish their corporate engine rather than spending the first two generations setting up. The game feels purposeful from turn one instead of spending early turns just placing infrastructure.

Ares Expedition is a separate standalone that redesigns the game as a card game with rounds instead of generations. I find the original more satisfying but Ares Expedition plays faster and is more accessible. For groups who love the Terraforming Mars theme but find the full game too long, Ares Expedition is worth trying.

Colonies adds orbital platform mechanics that create a new resource economy. Turmoil adds a global politics track that affects all players. Both are worth adding to your rotation after you have played the base game and Prelude extensively.