Okay, so I got to all the levels on page 3. So, long response time.
@Zero Revolution Damn, Off The Tracks was hard. But I really like it!
As for Secret of the Boos... I figured out what to do, but then I decided to finish it another time. Good Ghost House though, I generally loathe those in actual Mario games (I don't like puzzles in my platformer, usually) but the ones on Mario Maker are generally fun.
@Cuddlefish Those were tricky, except the Squid one.
@sayaka_abstergo Those levels you posted were nice! Especially Cap'n Olimar's Perilous Journey, that was a nice recreation of Pikmin's aesthetic in Mario Maker.
@Ink Gunner Emily Was Coursing the first level you made? Because it felt like a modified version of the tutorial level when I went through it. They're all good tho.
Also Lakitu let me skip the last half of What The Pipe? Was that supposed to happen?
@shy Fun levels. I like Shell Bowling, that's a nice idea right there.
@Noire I liked the haunted train.
Also, glad it wasn't too easy to get through Yoshi Must Live.
I hope I see more stars soon as well.
As for what I'd like to see in future updates to Mario Maker...
Slopes. I wanna make The Castle's Secret Slide in Mario Maker, and I can't be the only one. Also slopes are fun in general, so why not add them?
Poison Mushrooms. I wanna make a level that's just small Mario dodging flying Poison Mushrooms and Spiny bullet hell.
More power-ups. Specifically, Ice Flower as an across-all-themes thing, Frog Suit for SMB and 3, Tanuki Suit for SMW and U (acting like the 3D games' Tanuki Suit), and maybe Builder Mario (as seen on the cover) as a Hammer Mario for all themes.
More enemies, maybe some enemies that previously only existed in the 3D games could come on down to 2D. And the Koopalings would be a nice alternative to Bowser Jr, if you differentiated them enough (which they can, as NSMBU showed).
Luigi as his own guy, rather than just the Weird Mushroom giving you his physics. Also Peach and Toad, acting like they did in 2 and/or 3D World.
For bonus points, the Weird Mushroom gives Luigi Mario physics and makes him fat and shorter (so it makes him Marioish), it gives Peach a double-jump, takes away her ability to float and makes her look like Daisy (because why not), and it makes Toad even heavier, with a lower jump height and the ability to destroy blocks by jumping on them (and gives him Captain Toad's gear).
Finally, more level themes. Personally, I'd like to see Desert and Ice themes.
I doubt all of this would happen, but I'd like to see it.