The game contains a ridiculous amount of nods to other IPs. To say it's a tribute to gaming itself wouldn't be a lie... but not only games, there are also nods to various movies, songs and musicians, ancient myths, and even a few modern pop culture references. Many of the references are painfully obscure while some are blatant. Here's one spoiler:
In stage 1, the achievement "Hard To Handle", which is achieved by scoring an Infinite Combo, is only attainable by downing a large number of the black birds at once without being hit. The black birds are crows, which are often associated with Halloween, which is what stage 1 is themed after. This is a reference to The Black Crowes' cover of Otis Redding's song of the same name.