Cave Story was one of the first videogame that started the trends with retro games. However, Cave Story:
It has lots of catchy and unique music, not just generic tunes.
It has an history and it is not generic.
It has characters that feels living and each one has its own story and motivation.
It has a balanced difficulty (with the exception of the good ending). It is not just toss some insanely-hard-asian-level difficulty.
It has lots of details and secrets. The creator puts a lot of ♥ on it.
And it was created by a single person without any budget. Instead, we have a lot of 2d retro platforms that are simply shovelwares and it include shovel-knight (it was a really so-so game). Practically every 2d platform fall in this category with only a few exceptions. For example, if you want a hard game, then we have VVVVV, N and Super Meat Boy.
It depends on each person. But you can't deny that the creator of Cave Story put a lot on it. For example, the Littles (that they are really easy to miss), to get all the puppies, etc. For example, Curly's underwear. It has no purpose but for the lulz.
However, Cave Story:
Instead, we have a lot of 2d retro platforms that are simply shovelwares and it include shovel-knight (it was a really so-so game). Practically every 2d platform fall in this category with only a few exceptions.
For example, if you want a hard game, then we have VVVVV, N and Super Meat Boy.
For example, Curly's underwear. It has no purpose but for the lulz.
https://youtu.be/qD5kTWbrsHc
meh