Well, I picked up Super Mario Maker, obviously. I've made two courses and played a couple of levels made by others (many of whom seem to have done the "set your Wii U's calendar forward" trick to get more items.)
I'm a longtime Mario veteran, of course (Super Mario World was the first I really played seriously, back when the SNES was the current-gen,) but I'm pretty inexperienced in level design.
So far the two stages I've created are both pretty simple. The first is kind of two parts - one involves making tricky jumps between flying koopas and then kicking a shell through a long line of piranha plants (because it's just so satisfying and cathartic.) It's not a terribly difficult level as long as you know how to jump from koopa to koopa.
The second is practically an auto-play level (you do have to run forward,) which I recognize is a genre that will probably get pretty old. Still, it has you bouncing off of a ton of red flying koopas, which is pretty fun. There are a few superfluous bits there that I should get rid of, but it's not terrible.
At this point, without clock shenangians, the options are pretty limited. You can make solid ground, bob-omb-able blocks (though no bob-ombs,) destructible blocks, and question mark blocks. You can make pipes, put in super mushrooms and coins and those bouncing spring platform things. And then you can put in Goombas, Piranha Plants, and Koopas (the latter two you can shake to get variants, like the fire-ball-spitting piranhas and red "I don't run off platforms" koopas.)
And that's it for now. You can do a fair amount with these items.
In terms of themes, I currently only have the Ground and Underground settings and the Super Mario Bros. and Wii U "looks." (No World or 3.)
After playing for a while, my gamepad was getting low on battery, so I took a break. I'm eager to get the Super Mario World theme and the Ghost House setting (along with Boos!)
Next level I come up with I'm going to try to make a bit challenging (but not absurdly hard, like some people seem to do.)