Great idea. Mediocre-to-poor implementation.

The "Superpowers Game" engine doesn't play audio in anything but Chrome, takes forever downloading all of a game's assets as a million individual tiny files at page load before the game starts instead of even attempting to package them up in any way or stream any of them as needed, requires all available server-wide plug-ins to run any game built with it even if that specific game didn't make any use of them whatsoever, and sprite animations seemingly are all intended to use a fixed-framerate system that doesn't allow some parts of certain animations to play faster or slower as necessary for good flow.

The asset bundles are mostly decent, but fail to give you any direction as to how they are intended to be imported and used (in the case of sprite sheets with multiple animations packed together, for instance, there's nothing to mark or list where each animation starts or ends) and tiles often don't tile (for instance, the trees in the ninja adventure pack come in bundles of three and individuals, as if they're supposed to be able to tile properly to make any shape of forest -- but instead they're sized and positioned such that you can only reasonably use them as individually-placed objects which are probably going to be a pain to write collision code for and place enough of to make it look well-covered.) Since they're just raw art, any further nitpicking would be purely subjective in nature.