Sasuke's delight at his newly acquired Eternal Mangekyou Sharingan has always struck me as unusual and odd, since he describes Itachi's eyes as "sad" and "disgusting" and that they "weigh me down", all decidedly negative terms that most people would frown over rather than be excited about. Yet in the same breath, Sasuke seems gleeful that "these are good eyes".
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Sasuke seeming unusually enthusiastic and gleeful about something "sad and disgusting" interjects dissonance into the moment. Unless Sasuke is just using poetic hyperbole, his words introduce the notion that apparently each eye has a different "feel" to it, because Sasuke essentially states that Itachi's eyes "feel" different than Sasuke's own Mangekyou eyes did when he possessed them before he transplanted his brother's eyes to awaken the EMS.
This does have an interesting implication that each eye has a "feel" to it, not merely a physical feel but an emotional resonance. At least, evidently Sasuke senses an innate difference between his eyes and his brother's eyes, as if the eyes themselves carry memory and emotion in them, since Sasuke notes the many sad things that those eyes have seen.
This gives eyes a spiritual and sentimental significance, as if they hold the feeling of their user within them. I don't think that Sasuke actually gained any of Itachi's memories from transplanting Itachi's eyes - because that's not how it works - but Itachi's eyes evidently have a sad, depressing feel to them that Sasuke can sense.
Since Sasuke vocalizes his observation that Itachi's eyes feel markedly different than his own, since they are sadder and more disgusting than his own and carry the weight of all the disgusting and vile atrocities Itachi had committed and witnessed in life, Sasuke feels and senses that through the eyes. This implies of deeper connection to whoever transplants the Sharingan, as it gives them a closer emotional connection to the Sharingan's original owner.
As I've said before, the Sharingan are the eyes that reflect the heart, a visual symbol of an Uchiha's passion and the depth of their grief, their desire to protect, their love and guilt. So it seems natural that for a power that directly corresponds to one's emotions and emotional state, the Sharingan develops a unique essence of its own that other wielders can sense.
It's a neat and interesting concept; it's too bad we don't get much commentary on how the other people who transplant eyes felt about the difference between their original eyes and the transferred Sharingan eyes.
Because the Sharingan is essentially a physical manifestation of its user's emotions turned into power, perhaps the emotions contained in a Sharingan only hold meaning to those who were close to its user. It could even be that the Sharingan resonates best with the emotions of those who have love or empathy for the eye's original owner. In that case, perhaps Sasuke is only able to understand and comprehend the full weight of Itachi's Sharingan eyes because he was so close to Itachi. Though one does have to wonder what Kakashi thinks about Obito's eye and the feel of its essence, if it feels like anything. Though Kakashi is not an Uchiha and presumably not as well attuned to the Sharingan as an Uchiha would be, so perhaps he doesn't have the sensitivity to notice if it feels different.
But perhaps the emotions in the eyes determine how well it melds with another user, almost like the eyes will work better for a master who was close to their original user. For example, Kakashi was complimented for his finesse with the Sharingan and even became renowned for his mastery over the Sharingan. Perhaps it's precisely because Kakashi had a strong connection with Obito, so the emotions Kakashi had for Obito resonated with the eye and made it stronger and easier for Kakashi to use than it would have been otherwise, like if he had stolen an eye from some random Uchiha he didn't know.
Similarly, perhaps the reason why the Uchiha insist that an Eternal Mangekyou Sharingan must be gained from transplanting the eyes of a blood relative is because people tend to be close to their family members, and perhaps it's not the bloodline connection that's important but rather the emotional connection that the eyes resonate with. In Madara's and Sasuke's case, they were both very close to their brothers, so naturally their EMS would be quite powerful as a result. So maybe the EMS can be gained by transplanting the eyes of anyone that a user is close to. That would be more in keeping with the Sharingan's habit of responding to emotions, as it would mean that it resonated and advanced in power for any new user that deeply loved and cared for its original master. Or maybe EMS is awakened from both bloodline connection and close relationship, or maybe it's only awakened purely in response to bloodline connections. Who knows? We can only speculate.
