Someone is probably going to stab me (or at least get upset at me) for saying this, but why all the hype about Kerbal? I checked out the game, and thought to myself, "Build spaceships, try to get to space, fail over and over... this does not look fun. At all."
What is making it so absurdly popular?
It's an "easy to learn, hard to master" thing. The nature of the game is such that there is always something you can do reliably, and always something that's just out of your reach. For example, right now I can consistently land and return a mission to the moon, but I'm still working out how to get a ship to another planet. In addition to that, it's a very satisfyingly mental game. When you reach a goal, it's because of the thought you put into your design, your orbits, maybe some tricky flying to land on a hill, etc. Your designs are either tried-and-true or totally experimental, but either way they're things that
you made, so when everything works out it feels like a real accomplishment. There is always room for improvement and experimentation, which is a rare quality in a game. Failures give you ideas about what to do differently rather than just making you repeat things. In short, the game is about teaching yourself how to manipulate a system which is comprehensible but still complex enough that you'll never have complete control over it.
Of course, it's not everyone's cup of tea. Personally, I love that KSP
exists and I've had a lot of fun with it, but I don't find myself playing it very often. The level of investment involved can be unappetizing when you're trying to relax or don't have very much time.
Also, hey, what about that 40% off Spacebase DF-9, huh? Is that game any good? I haven't really heard much.