Mario, with an unlimited number of levels available. Now I didn't say they would all be good levels, but even so the chances are good that you already know if you're interested in this or not.
The creation toolset in Super Mario Maker is a pleasure to use. It is simple in a way one would expect from Nintendo. Easy to understand but with so many variations and combinations there are seemingly endless possibilities. Unfortunately your possibilities are limited when you start the game for the first time. You only have access to 12 of a possible 60 placeable items or blocks when starting. In addition you may only use two of the four game styles, or two of the six backgrounds. This is probably to not overload, get comfortable with these things and you'll be ready for the full editor! If you have ever played a Mario game before, or are over the age of 7, you can probably handle things faster than the game dishes them out. The metric for deciding when you get new 'deliveries' as the game puts it seems to be putting roughly 5 minutes into the editor and placing some amount of items or blocks into the level. Spam enough and you will be told a delivery will happen in the future. Spam your little heart out (using blocks that can be placed by dragging the stylus, not tapping, helps a lot here) and the delivery will arrive 'sooner than we expected!' Rinse and repeat until you have the items you really want to play with and/or everything unlocks. If you are a more patient person I believe just opening the editor a few minutes everyday for a week should get everything unlocked.
Frustrating unlock method aside, using the editor is fantastic. One of few games to use the gamepad well drawing blocks on the screen feels great. A large hand will appear on the TV to let people in the room with you see what you're doing (clicking in the sticks will change to be left/right handed, change skin colour, or be a cat or dog paw).
Many items can be changed into an alternate form by shaking them around the screen, for example changing a green shelled turtle to have a red shell. Not everything has a second form, but having it be something you can only find out by placing it and then shaking, means you will probably try putting everything in a level at least once. Enemies and items can also be combined; give a Goomba wings or a mushroom to make him huge, put a turtle in a question block instead of coins. There is a lot of fun to be had with subverting expectations of things that have been set in gamers minds for so long.
With a hit of the select button you can switch between editing and playing the level, starting wherever you put Mario. Pop back out to the editor and you can (after unlocking it!) see a trail of ghost Mario's where you have been. Useful for planning out jumps or enemy distributions. Iteration can be very quick, it's very satisfying when you get a moment of inspiration and quickly make it happen.
You can create Mario 1-1, although sticklers might care that you can move the screen to the left now. Pipes that go to other backgrounds are possible, the length of the stage is variable, the time limit can be changed, and if you're a monster you have 3 speeds of auto-scrolling to choose from. it's possible to create an abomination of a level with everything available, but at least the creator has to be able to finish their own level before it can be uploaded for everyone else to suffer through. Many levels, especially at this early stage, will be full of things just because they can be. Most real Mario games don't throw that much at you at once, and that kind of restraint will hopefully be learnt by the community. Of course the living nightmares some people produce are fun sometimes too.
There are also 100 costumes that can be placed, taking the form of a question mark mushroom to put in the stage. These range from Luigi, Toad, and Peach to different Pokemon or even Megaman. They are costumes as they do not offer any change in gameplay. Effectively the game thinks you are super Mario, if you get hit you become small and the costume falls off. They can change sound effects and the end-level music (hearing Sonic's end stage music caused my brain to melt). Some offer iconic poses if you hold up or down on the d-pad. These costumes can be unlocked right away if you have the relevant amiibo, otherwise you unlock them by playing user generated levels. More on that below.
For many people, most I would wager, the appeal of Super Mario Maker is a 2D Mario with an endless amount of levels, not the ability to create them for themselves. Past a few initial experiments, the general population will just want to play.
There are a few different avenues here. The 10 Mario Challenge gives you 10 lifes to complete 8 levels. You may earn extra lives up to a maximum of three per stage, and you can never go above 10 in total. The stages in this challenge are all pulled from Nintendo, and after three or four runs through, I started seeing repeated levels. They took full advantage of the tools and systems they have created, and show some good examples that will hopefully inspire people to get real weird.
The 100 Mario Challenge is similar in concept but pulls from the user created pool. You can play at three difficulty settings, with easy having you complete 8 stages. Normal and Expert require you play through 16. If a level is giving you trouble you can swap it out for another one, with no penalty. How Nintendo is sorting levels into the different categories is a mystery, but one assumes it has to do with pass/fail rates, so this will hopefully get more accurate as time goes on. When you complete a run of this challenge you unlock one of the mystery mushroom costumes, so you don't have to buy amiibo to get everything but it will take awhile.
Instead of playing one of the challenges you can play individual courses one after the other by choosing them yourself. This method of finding levels does leave something to be desired. You can look at the top rated levels, those featured by Nintendo, or a new and upcoming category also exists. You can also look at the top rated users, or those you follow and go through all of their creations. Levels are rated simply by giving a star or not after completing it, there is no negative feedback, this is Nintendo.
Unfortunately those are all your filtering options. The only other tool at your disposal to find stages is entering a course ID, a 16 digit alphanumeric code. While nice to share specific courses, it would be nice to be able to search by name, or game, or no water levels, or no auto-scrollers etc. Maybe that can come down the line.
You can get notifications for when people play your course, give it a star, or comment on it through Miiverse. You start with the capability to upload ten stages, with the promise of more slots if you get lots of stars on your levels. Looking at your uploaded courses shows how many people have run it, how many gave a star, the percentage of attempts that finish, and even a nice map of where everyone died, which seems a great tool if you're trying to refine a stage. You can download stages to look at in the editor, but if you try to re-upload it you are denied, stopping low effort copycats.
Super Mario Maker is a fantastic level editor, and is already a fun crazy Mario game with only a couple of days worth of user generated stages. People always amaze when it comes to user generated content and surely this will be no different, I look forward to checking in every so often to see what people have come up with, whether it be bizarre things never thought possible for Mario, or just genuinely good platforming challenges.