I think he did this more in his second term. It reminded me of the way Muhammad Ali spoke a lot slower in his last interview with Parkinson; and we all know why that was! But what's Obama's excuse? I get how slow speaking can be effective sometimes if used sparingly. But he went over the top. He was a great President though.
Yes, he was a good president. Speaking slowly was just his style, that is all. He thought carefully about what he said, unlike most people. That's what made him good!
the only thing he overdid was making too many concessions to what fallowed when he first got in and had congress with him and didn't have to. he reached out to the fascist pretending to be conservative element and they bit off his arm. how he talked, making clear that he did in fact consider and take into consideration, every conceivably pertinent factor, i would call that one of his strengths, really.
His college roommate, then an artisan baker in Greensboro, NC, described him in a TV interview as "a Hawaiian surfer dude." So his slower speech patterns might simply be his natural style.