Some time ago I suddenly realized I could indentify those who had studied Chassidus and who hadn't. When I hear people give publicd sermons, I can distinguish with a very high rate of precision. Even when I talk to others personally, I can make this distinction quite accurately.
Since this sudden realization I started asking myself as well as some of my Chabad teachers and rabbis how Chassidus seems to affect its learners. I haven't been able to indentify this seemingly profound effect and its putative components yet in a way I can formulate them rationally and apply this generalization to every new person I encounter. But at least suprarationally I feel the effect - or lack thereof - of Chassidus on its learners without knowing clearly why I know. Every time I asked someone, "You haven't studied Chassidus, have you?", I was right (and he was surprised I knew this.
Instead of continuing to ask myself the above question I occupy myself in the meanwhile with a much easier - but probably more meaningful - question, which is how the study of Chassidus, or to be more precise, Chabad Chassidus, seems to have affected me.
Before being exposed to one of the most important teachings of Chabad Chassidus four and nine months ago and then started learning it formally and privately, I received formal Jewish education in the Talmud at a "Lithuanian" haredi (i.e., non-Chassidic) yeshiva in Jerusalem and Musar in a small group guided by one of its few preachers-cum-practioners. This prior study of what is so different from the teachings of Chassidus has helped me appreciate Chassidus even more.
In parallel with Chabad Chassidus I've also been studying teachings of non-Jewish nonduality from works of masters such as Eckhart Tolle and Adyashanti. So the inner transformation I seem to have undergone may not be solely thanks to my study of Chabad Chassidus.
Probably the most important positive change I can identify in myself in comparison to how I used to be until about five years ago is that I don't identify myself with my thoughts, or to be more precise, thoughts of my ego. I can see them as replacable garments and treat them accordingly. Now I'm fully aware that I used to be fully asleep in that I was deeply trapped in the prison made my ego, which naturally caused countless problems in my interpersonal relationships in my both private and professional lives. In retrospect I can "console" myself by telling myself that those I collided with were mostly no less asleep.
Awareness of a problem is a half solution to the problem. Since I liberated myself from my mind-made prison, at least partially, I started to feel more peace of mind and joy as our natural state as the sun continues to shine even when it's cloudy. It still occurs from time to time that I'm temporarilly hijacked by some negative thought of my ego, but I can generally notice and neutralize it immediately afterwards, thus saving myself and others a lot of unnecessary suffering.
Another, no less important, change is that I have no blind faith any more in our intellect, which seems not to be but a tiny part of our human faculty. With this change came a fundamental shift in my interest. I'm more interested in life wisdom than purely intellectual knowledge, and in suprarationality than rationality (but with an anchor in physicality).
I've been extremly lucky to have been blessed with amazing teachers and rabbis of Chabad Chassidus in these four years and nine months. I've always been able to see living examples of how profound teachings of Chabad Chassidus are - and can or should be - applied to our daily life, especially in our interpersonal relationships.