The first would be great songwriting--in the sense that when you strip the song down to just chords and melody, its still a great song. This could be due to a few reasons--a memorable melody or form, interesting harmonic movement, or lyrics.
Secondly, I think its very important to try to do something new...some sort of musical idea that nobody else is really exploring. This might be an interesting use of rhythm or harmony, but I think that more often it is a sonic exploration. Timbral and production choices are defining bands' sounds more than ever. Often I hear songs that can be very interesting from a production or tone point of view, but the song itself is musically boring or stagnant. That's not necessarily a problem if the production and tones are sufficiently interesting, but I think the best songs are those that combine new sonic ideas with great songwriting.
評価ありがとうございました。@shamash