Celestia is a remake of Cloud 9 using a similar theme. Players ride an airship, taking turns to be the captain. The airship travels from one cloud city to the next. At each city, each player may individually decide to alight to score points, or to stay on board, hoping to travel to the next city to score even more points. There are perils along the way. Each time the airship attempts to travel to the next higher city, dice are rolled to see what cards the current captain needs to play in order to arrive safely. If the captain fails to play such cards, the airship is forced to land, and everyone still on board scores no points. So this is a push-your-luck game. After a trip ends, whether due to a failed flight or due to all players having decided to alight, a new trip starts back at the first city. This goes on until one player accumulates more than 50 points from the scoring cards he draws. There is a deck of scoring cards for each cloud city, and the scores vary even within the same deck. However generally the higher cities have higher valued cards.
The captain must always steer the airship to the next city if he has the right cards. He may not run the airship aground to deny other players points, albeit at the cost of not scoring any points himself. The only exception is when he has jokers in hand. Using jokers is optional. If steering the airship successfully requires playing jokers, then the captain has the choice of whether to steer the airship to the next city.
The game comes with some special ability cards. E.g. one allows you to force an opponent to alight. Another one allows you to alight safely when you otherwise can't.
The game components in Celestia are much prettier than those in Cloud 9.
The player pawns are different not only in colour. They are of different sculptures. We were a little clumsy so our pawns look like they are drunk.
Celestia doesn't have a game board. These oval shaped tiles represent the cloud cities the players are attempting to reach. The cards on the right side of each cloud city are the scoring cards.
The basic cards in the game, which are used to steer the airship to the next destination.
Celestia is a risk-taking game. You constantly face the dilemma of whether to score points now, or wait and hope to be able to score more, at the risk of scoring nothing. The passengers can see the captain's die roll before deciding whether to alight, so you know roughly how much risk you are taking. You should try to remember what cards your opponents are lacking from previous failed trips, however you won't know what recent cards they have drawn. These more recently drawn cards may just be in that colour they were missing earlier. You can look at how many cards they have in hand. More cards mean better chances of them succeeding, but again, you cannot be exactly sure whether their hands are very lopsided - many cards in one or two colours and none in others.
There is one consideration which I think most new players will take some time to grasp. You need think a few turns ahead, to see when you yourself will become captain. The captain normally doesn't have the option to alight. If you are going to be captain next, and you are down on cards, you'd better alight now, even if you are sure the current captain can make it to the next city. If you don't, you will likely end up scoring nothing due to being stuck as captain next turn and not having the choice to alight.
The special ability cards can be very powerful if used at the right time, e.g. forcing an opponent to alight when you expect he will be making a killing in the next turn. They can also help you score big if you set up such an opportunity.
Scores are secret, since you draw scoring cards and keep them in hand. So when we played we couldn't tell exactly who were about to win, or when. The number of cards and types of cards drawn only served as a rough estimation. Dith won the game handily. He drew quite a few high valued cards.
Overall Celestia is very similar to Cloud 9. It is only in execution details that they differ. Ideally what you want to do is alight just before the voyage is forced to end, but doing this consistently is a challenge. Sometimes you play safe and end up scoring much less than you could have achieved. Sometimes you get too greedy and end up scoring nothing. This game is easy to teach, and it's suitable for families and casual players.
I prefer the Cloud 9 version. It is simpler and cleaner. There are no special ability cards, which I feel is unnecessary and doesn't justify the additional complexity. I also prefer how the jokers in Cloud 9 work. You just need one joker card to navigate successfully. A single joker card covers all card requirements for the next leg of the trip. In Celestia, the joker is weaker and counts as just one wild card. So in Cloud 9 there is a bigger uncertainty due to how powerful the joker is. I like this. It's more exciting. There are more surprises. Cloud 9 is a better family game. Celestia seems to have added more stuff to please the gamer crowd. I can see the advantage of the scoring card mechanism. You won't know your opponent's exact score, and you can't precisely predict how much you yourself will score. This reduces tedious calculations at end game, since you can't calculate accurately anyway. Also, drawing cards is always fun because of the anticipation and the surprise element.
This comparison I'm doing is futile though. Cloud 9 is out of print, so if you like the game, just go get Celestia.