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 ton 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...make sure to click 'expand' to see these in full detail: