Your biggest challenge in programming games that "look" easy is AI. A lot of the challenge in an RPG or adventure game comes from how smart the enemies are, and all that stuff is very difficult to program and test - so don't do it. The same goes for math, don't mess around with noise functions and procedural generation. What you need to make are games with predictable, set challenges and premade assets. Things like Tomb of the Mask, Flappy Bird, Angry Birds, Tower Defense games, etc are all examples of easy-to-program games