Mario Maker is as super simple to use as it looks. Paint objects into the level, drag pipes to stretch them, tweak things like changing the direction of moving platforms, and then press play to, well, play. The only hard bit is trying to get through the absurd level you just made.
Even in the E3 demo, which Nintendo plans to add to, there was an appreciable level of customization. There are little things like giving wings to the goombas and koopa troopas or putting piranha plants into pipes, but also the major mechanic of being able to switch your level from old-school Mario to the New Super look in just one click. The issue I had was the amount of available space, which seemed a bit short; negotiable without obstacles in seconds rather than minutes. Again, maybe that's just the limitations of the E3 demo.
We'll all get to meet our Mario Maker when it comes to Wii U next year.