For me, it is the thought process that he puts into the paintings that really turns me on to his stuff.
I didn't like Picasso at first but nonetheless went to the Picasso Museum in Barcelona when I was fairly young. The first charcoal sketch I saw was of a Roman/Greek bust that jumped off the paper. (Really popped!) Like nothing of his I had seen before. After viewing a few I realized they were drawn when he was 12 which blew me away.
I soon realized that the museum was arranged in chronological order which allowed me to see his thought process in moving through each of his periods and ending up with the style most of us are familiar with. And then it made sense to me.
A week or so later I went to see his Guernica at the Prada in Madrid, which at that time was housed in a separate building. A long series of entrance halls were lined with case studies that evolved in both major and minor ways throughout time. Then you turn a corner to the big reveal of the culmination of that thought process; the massive finished piece where everything you just saw, and the evolution that went into it, was shown. I must have spent at least an hour in there.