Since 2006, over a dozen artists from a Mario forum collaborated on a number of eBoy-esque isometric Mario worlds, like the one you see above -- and the results are pretty fantastic.
The long, curious history of the Isometric collaborations on the Mario Fan Games Galaxy Forums is documented on this Wiki, if you're curious -- just know that it took a lot of coordinating, some hiccups and lots of creativity to bring these to life.
As for the first image -- there are a lot of references there. Here's the full thing. Can you spot all the shout-outs? Make sure to annotate when you see one!
Here are the rest: