Really nice concept!
I don't think I've ever played a game that combines golfing with orbital mechanics, but I think this game proves it can be a really great idea! I played about 5 levels or so before getting stuck, since my moon landed on a planet that was rotating around the star so fast that I could no longer click on it, which judging by the other comments is something other people also struggled with. Making sure that doesn't happen should be very easy to fix though, just make the hitbox of the moon super big (or allow the player to click and drag from any cursor position, since you are showing the 'guide line' anyway).
The second common point of criticism the other commenters have, if I have understand the game correctly, is that the guide trajectory is calculated under the assumption that all other celestial bodies remain static, right? That's why some players feel misled, because as the moon follows its trajectory, it is experiencing a different gravitational field at each point in time, instead of the original trajectory previewed when time was 'frozen'. This point is a bit more tricky to fix, and I think there are two extremes: Either your original way (minimal assistance), where the player has to predict the path of all celestial bodies and guess what the gravitational influence on the moon is going to be at each point in space/time, or (fully assisted) your preview calculates the actual 'dynamical' trajectory and the player only has to find the correct alignment of bodies, pitch, and amplitude. I think neither of these two options are ideal, since the fully assisted mode only requires the player to predict the ideal point in time to click and can then obtain the trajectory through trial and error without using any tries (and thus makes for a less compelling game). A compromise would be to convey additional information to the player, e.g. by drawing notches on the guide line indicating the moon's velocity (the player can count how far the moon would get in x frames) as well as notched guide lines predicting the orbits of all the celestial bodies (so the player can judge how far they will have travelled in x frames). Finally, you would also give the player some visual indication of how strong the gravity of each celestial body is (e.g. by drawing concentric circles at certain threshold values).
I think this game definitely holds promise and is worth working on in the future (if at least to fix the controls, such as by making the camera movement much smoother/more responsive) and I hope that my ramblings can be of some use to you!