I recommend Unity. It's about as beginner-friendly as it gets, and you can see results fast. My brother and I have both had a blast playing with it. If you already know how to code, you can probably do a lot with it.
As an experienced hobbyist game developer, I find Unity to be an incomprehensible airplane cockpit of bad UI.
For the kind of game presented in the article, Gamemaker Studio would be more reasonable. Unity has a lot you don't need, which obscures the path to making something simpler like this.
I'm sure there are other good options too. I think there's a JS-based platformer-oriented engine out there.
