((Well, if you want to go in Order: Act 2 and then Act 1. Really, these guys make me love Dr. Light so much more than the games ever did--I pity him so much in this. XD Wily took his work, his love, blamed the murder on him, became Big Brother, killed the only man who had hope in freeing the city, killed his son (Protoman), and by Act I 's time his second son (Megaman) is rising to oppose Wily.
X4 was one of the few games I did not finish. XD The only Megaman I was good at playing was Legends and Legends 2. I got to Sigma in X1, but I honestly could just play Storm Eagle's stage all day because of that music. xD But if Zero follows the path of Protoman, if these guys ever wrote an album based off Megaman X, it would be so much worse... ))
((It was stuck in my head all last night too. XD I was singing Joe's part (the first verse; Dr. Light is the deeper voice in the second verse). Really, I suggest checking them out; the First Act is far more dark and gritty with the music, while Act 2 serves as a prequel. My favorite song from Act 1 is The Stand. Even the story of both albums is really good... Act 2 makes me appreciate Sniper Joe so much more now too. XD
All I can imagine is what is going to happen if they ever decide to continue the story (There's a third Act in the works, I know) after this by adapting Megaman X. XD That series was already pretty dark to begin with.))