To make Made Invaders feel more like a real-life video game, we included some event sounds and game music. Originally, we had been using the Adafruit VS1053, which unfortunately needed to be continually polled to keep playing mp3 files in our setup. With the main controller having to poll the sensors, updated the scoreboard as well as poll the music player at regular intervals during play, it was all looking a bit too complicated.
The SOMO-II MP3 decoder looks like a better alternative then; connected by serial (so fewer wires than the VS1053), able to play in the background, the main downside is that I couldn't find a pre-made Arduino library for it. While there is an example sketch online, although the functions used were a bit limited so we built a library.