Everyone's different, and fathers vary, of course. But I certainly read significant emotion in the letter.
I have no doubt this ordeal has been excruciating on the elder Snowden, as he helplessly watches the international bartering for his son's life and freedom. What I find admirable, and where the emotion and strength lies, is that there isn't the slightest hint of wavering in the father's resolve--no pleading, no hand-wringing. An incredible gesture of thanks, loving commitment, and support.
I have little doubt it will impact Snowden in much the same way it did me.