There are always two ways to look at a song:
1) What the average listener hears. This usually defines the song in terms of its genre, its cool factor, etc.
2) What musicians hear. This involves some of what Hectic said: chords, production, lyrics, etc.
Great songs don't have to rate highly in both categories. Great songs can be easy to play, or they can require virtuoso skills that may not sound complex but are incredibly hard to play. I'd guess that Limelight score a little lower than some Rush songs in category 1 (although it's a great song, nice crunchy riff) and is right up there with some of Rush's more difficult stuff in category 2. Being a musician, Hectic is going to weigh category 2 more heavily.