It's the lack of music. I've tried to put my finger on it for a while and I figured it out. No music during the lightsaber battle, the Rebel Base before the Battle of Yavin, the beginning of Obi-Wan and Luke talking in his hut (always felt like this needed the music the most because you hear these sounds in the background and it's very distracting), and I think there was another scene but I can't remember. You had a whole slew of music in the rest of the OT and PT. There was barely a moment when there wasn't. So I think that's the reason why A New Hope feels a little disconnected in a way.