I felt almost exactly the same about Rymdkapsel; I knew nothing about the gameplay before downloading it, so the process of learning what it was and how to become good at it was super-interesting. After my first defeat, I knew what kind of things to do in order to become more efficient and research all of the monoliths in time, and the process of doing that was still engrossing and fun. When I died after doing that, though (And after completing the achievement for reaching wave 28), I felt almost no motivation to go back and complete the final achievement. I think this is down to two things: While the challenge increases with every wave, the nature of the challenge never does. It's always the same enemies, and the process of defeating them is to simply move guys into weapon rooms. Secondly, the time between waves decreases to the point that you eventually have no time to regroup and improve your base, so it ends up that what you do in the early game (Choosing the layout of your rooms) becomes the most important thing in the late game. This is also a problem I have with certain Tower Defense games, where you have to strategise across an entire hour-long play session, and the game just ramps the difficulty up and up until you invariably die. I like this kind of thing in games where the average play time is much shorter (Super Hexagon, for example), but when each game takes so long, it can be hard to motivate myself to start from scratch again.
That said, I did really enjoy the time I spent on Rymdkapsel, and I do think people need to play it.
