Spaceflight Simulator is a sort of a sandbox game, in which you get to design your own space rocket and explore the solar system. The game area doesn't go much farther than Mars, but even so, there are plenty of challenges to overcome before you'd even consider going that far.
You start the game by building a rocket ship. You get several ship pieces, but there aren't many ways in which you can combine them. Several fuel segments can be stacked on top of each other while a booster needs to be attached at the bottom. Yo can place several of these rockets in parallel using connectors but you can also stack rockets with detachable separation rings. The important thing is to place a command module somewhere on top, in order to have control over them.
The controls are rather simple, although the game itself poses a nice challenge curve. Unlike the Apollo astronots (typo intended), you are spared from analyzing a bunch of vector data to get your bearings. Instead, you can examine your vehicle and the surrounding space in two view modes. The regular view lets you admire it and gives you detailed control over individual engines, separation rings, connectors, landing gears, and parachutes. The map view lets you examine orbit trajectories, and also displays departure opportunities for reaching your designated destination target.
Spaceflight Simulator uses a simplified physics system that, albeit being completely 2D, still takes into account atmosphere, gravitational zones of influence and slingshot mechanics. The interface anticipates your trajectory for when it reaches a planet or moon's area by showing a localized orbit curve. The orbit might not make sense if your ship is still too far off its way, but it will clear up once it meets the general trajectory line.
Letting aside the fact that you will certainly spend a few failed attempts at even reaching Earth orbit, getting to the Moon requires you to turn your circular orbit into an ellipse that's wide enough to reach the path of the Moon. Even then, you will need to synchronize the ellipse's apogee with the future position of the Moon so that you can have any chance at approaching it. Sounds daunting, doesn't it? Luckily, the visual aids in the Map view are enough to let you know if you're on the right track. However, whether you still have enough fuel to complete the job rest solely on your rocket design and your skill at conserving thrust. You can also save the game at any time, so, you can set up checkpoints, like having achieved Earth orbit, or being on a nice descent towards the surface of Phobos.
Now to some criticisms. Although the camera angle is mostly fixed, the direction indicator often turns up showing the wrong way, which makes it unusable, unfortunately. Some other problems include automatic detachment of the command capsule without any player input (more reason to save at key points) and graphical glitches during planetfall. These don't happen on a regular basis however.
It is quite astonishing how a minimalist game can evoke such awe and recreate the heavy gut feelings that are associated with space travel. Too often space themed productions, be it movies or games, treat space transit like sailing the seas. Admittedly, although you need a real Faustian spirit to traverse the Atlantic with only a vague idea of what could lie beyond, launching yourself on top of a rocket to navigate through void and onto a moving orb is a whole different ball game. I suspect that if you enjoy games like Kerbal Space Program or Orbiter, you'll most likely enjoy Spaceflight Simulator. It's infinitely simpler than KSP, but it's worth checking out. Godspeed!