Ganymede features a bite-sized action system popularized by games like Splendor. Each turn, you have one of three options:
• Draft a settler tile, which adds a settler to Earth, moves a settler, advances you in reputation, or lets you draft a settler ship to Ganymede.
• Draft a shuttle card to move settlers from Earth to Mars or from Mars to the settler ships in orbit around Ganymede.
• Discard 1-3 settler tiles to take 1-3 basic actions: getting a settler, moving a settler, adapting a settler, gaining reputation, or drafting a settler ship.
As you take these actions, settlers shift on your player board from Earth to Ganymede, changing the value of everything available for drafting since the shuttle cards have specific costs to use — and by "costs", I mean settler requirements. Settlers come in four colors, and an Earth shuttle might specify that it will move two red settlers from Earth to Mars, or perhaps one yellow settler, or a blue settler along with a settler of any color.
Logically this makes no sense, but also logically you can realize that you're playing a game and not actually shuttling people to Mars on a color-exclusive basis, so don't worry about it. Everything is done in service of the game; if the shuttles could take anyone, then the only challenge to the game would be winning the right to take the first turn.
Shuttles from Mars to the Ganymede orbit have similar color restrictions, and to launch a settler ship from orbit to the surface of the moon, you need to have three settlers of the same color aboard or one settler of each color. Again, don't think about that too much. You have two settler ships to Ganymede waiting on your board, each with a way to score points — sometimes a fixed value of 4 or 5 points and sometimes a variable amount depending on the shuttle cards you draft, the number of settler tiles you have, and so on. Many settler ships have a bonus of some type, such as giving you a new settler on Earth once it launches.
The game ends the round that someone launches their fourth settler ship, and this can happen sooner than you think as actions can compound themselves. Settler tiles come in four colors, and if you draft a tile in a color that you already have, then you take two actions with the new tile instead of only one; if you already have two tiles of this color, then you take three actions. Shuttle cards work similarly except that they come in five colors. Most shuttle cards have a bonus action on them (gain a settler, move a settler, gain reputation, adapt a settler to a new color), and when you draft a second card in a color you already have, you take that bonus action twice. Bang, zoom — to the moon!
In addition to those bonuses, when you draft a shuttle card in your fifth color or when you top out your reputation track, you immediately launch one of your settler ships, regardless of how many settlers it has aboard.
Your challenge in Ganymede is how to put everything together to get the most out of every action with nothing being wasted — and the game design is set up to hamstring you as much as possible along the way, thanks to the color restrictions on the shuttle cards, the launch requirements for the settler ships, the settler limits on planets (six on Earth and five on Mars — they like a lot of room to themselves), and of course your fellow players, who will take tiles and cards that you want.
Unlike in Splendor, you can't hate draft a shuttle card just for kicks; you must be able to use a shuttle card when you draft it, but given that only four colors of settlers are in the game, you often have situations in which you worry about someone else grabbing the shuttle or settler tile you need that's key to your next couple of turns. You can't plan ahead too much given that you're relying on a small pool of tiles and cards — only four of each — but if you play with only two players instead of four, you do have more opportunities for four- and five-turn plans since only one other person is present to mess with you, with the discarding tile action being akin to a "Get out of jail free" card as it allows you to create the tile or card you need that isn't currently available. This action isn't ideal since you reduce your ability to gain settler tile bonuses, but sometimes you need that last push to get all the pieces in place, so don't forget that it's available to you when trying to puzzle out how to launch that final ship...
(Ganymede was released in mid-2018 in Europe by Sorry We Are French, and the game will be available in North America in Q1 2019 thanks to Lucky Duck Games. I've played five times with all player counts on a copy from the BGG Library.)