For me its a simple one, after chancing upon the dharma, am i still interested in the same things i was when i was 10, 20, 30 soon to be 40. Has my mind calmed down, not so jumpy at lifes distractions, do i still seek pleasure in the things that gave me pleasure in the past. if i say yes, then buddhism hasn't change me much at all.
But if on the other hand the changes are there, the mind feels soft, the heart less tense, and my pursuits more in seeking outwardness (ie. for others, with others, on behalf of others) vs inwardness (internal focus, self focus, grasping, fear, loss, depression) I would feel buddhism is changing me.
Over a small period of time the differences are not noticeable but like glaciers over a longer period we start to see big changes. Its all perspective. What happens if change is too fast?! Anyone ever have a breakdown from getting into buddhism?
been there, done that.
It often happens when the person only has theoritical knowledge of Buddhism and the Dharma. The breakdown happens when that person realizes that he/she wasted his/her time for studying only and that is wrong and incorrect, not Buddhism etc. After this process, real change will start.