The most important attributes that I strive to perfect (in a song) is smooth transitions, melodic progressions, and most importantly.....the ability of knowing when NOT to play too fancy. I write alot of old - new metal type music and I listen to a vast, wide range of metal-type music and each extreme of it gives me different angles of influence. When I'm writing music, I don't sit down with my guitar and TRY to write it...it all comes naturally. I don't usually write an entire song, one after another... peices of music will pop into my head, or I'll like something that I was playing when I was just screwing around. It's not until later until I can start peicing parts of music together carefully: I'll think *hey this goes well together with THIS thing I wrote the other day* After that, I will come up with something that can smoothy transition the two parts together. Days or even weeks can go by before I have completed an entire song..heck.. even months sometimes - I have recalled things that I wrote 2 years ago to correspond with material that I came up with a week ago. The reason why it takes so long for me is because I tend to write parts for 2 guitars for rythm\melody\harmony\etc. as well as drum beats - I've been a drummer since I was 3, so the beats come naturally as well. I'm not so much on lead, not because I don't and cannot play decent lead (I do come up with leads that I think are great, but they stay in my mind because I can't play them for beans) but because a song can still be a good song without lead.
A good song isn't about flaunting skill, but about the structuring of the song as well as the contrast in timing, rythm, and\or notes. When something isn't played often, and when it's played, its appreciated. If its played all the time, you get sick of it. You don't want to be redundant.