I also find his eagerness to learn and lack of guile quite charming. I love his demeanor when being taught to dance by Beverly in Data's Day
. The whole scene is beautifully done.
And sometimes it's the tiniest things that I enjoy. Once in a while he does something so...human (for want of a better word) that you cannot believe that anyone would ever doubt his sentience. I think it's also in Data's Day
when he is sitting at a work station thinking to himself and he catches his finger tapping...I don't know why, but I love it.