You really need to get another set of headphones with both earbuds to hear these man. :) My mixing technique is VERY stereo. To illustrate what you are missing out on when you listen to only one speaker, I present the following diagram. :)
L=Hard left speaker. Meaning there is not even an echo of it coming out of the right speaker. C=right in the center. R=Hard right speaker
Here are the guitar parts (every song has 3, occasionally there may be a random 4th one that generally just plays some fancy unnecessary overdub) as they appear on the stereo image.
Guitar 3, the one smack in the middle usually plays the melodies, and/or solos. Guitars 1 and 2, which generally play the riffs and chords are hard left and right. They are usually playing the same thing so having them so far apart gives the mix space to breathe while at the same time making the riffs sound really thick and chunky.
However, anytime there is harmony or "dual melody", It switches up in an instant, and the part that was playing the main lead is now playing the rhythm part and the two parts that were playing the rhythm are now playing the two leads. I do this to make the harmony's stand out and sound clear, since in a dual harmony situation they should take precedence over the backing part. Two leads sortof overshadow the rhythm part, which is how it should be. But having two rhythms doesn't over power one lead because since they are playing the same thing it doesn't stand out to your ears as much so it's balanced.
May seem a bit of a weird set up, but trust me it's the way to go. I've experimented with having everything a little closer to the center and it just sounds muddy and takes away the punch.
So, in listening with only one earbud, you miss out on ALL the dual harmony parts and only get one of the melodies when there should be two. And there is one of those in alteration.
And not only that, but the riffs will sound weaker and/or thinner to you because there is meant to be an entirely different take of that riff playing at the same time.
And that concludes my thoughts on the matter. Regards. :)
^ Needs to pull the stick out.