I get the comment on the experience of the video, but perhaps it's just a musical distaste thing. I didn't mind the cover, love the original, but I didn't see it detracting from the constant bleeping of the interface and the repetitive battle music.
To the OP, grats on your kill and don't listen to the BGM zealotry. :)
Well I think it comes down to what the video is supposed to accomplish - that is, what it is supposed to be. Is it intended to be a video of someone's fight with a boss monster from a specific game? If so, then the focus is on the game itself and the intended audience is people looking for more information (strategies, etc.) about the game. Or is it intended to be a video about something else in the game, showcasing a humourous occurrence or a dramatic victory in which the focus would be on the characters or the setting - only more generally dealing with the game itself.
Indeed: does it show a strategy - or does it tell a story? The former should have the least amount of intervention possible: the focus is on game and game mechanics; the latter can have all the new voice-overs, cuts, music, and effects it desires, for the focus is on something besides the game.
Look at it this way: if someone uploaded a video of "the final cut-scene," should it feature the original music, sound, and visuals? If someone uploaded a video of "an RP session with my friend," does it matter whether the original music, sound, and visuals are completely preserved?
Ultimately one could argue that it comes down to taste, but I know that when I
look up "Fight with Jumbo Cactuar," I'm not watching the one with the Fallout Boy (or whatever the uploader's definition of "kicka$$ music!11" is) loop.