Maybe changing my mind from my first post, but it seems to me that the quality of "good" VGM is that it fits the game and the scene well. Obviously if the Green Hill theme was in a game like Bioshock, then it doesn't do it's job as a supplement to the video game itself. Therefore, one could consider it "bad." HOWEVER, this all depends on whether we're analyzing these as compliments to a video game or as individual pieces of music themselves. In the latter case, you could argue that many modern day songs are grand in production, but lack a compositional aspect that makes them truly great and memorable. It doesn't have to be catchy per se, but if you forget a piece of music shortly after hearing it, then it must be lacking in some regard. It is the good pieces that you remember and want to hear again.