Visit to Krypton. In the novelization they describe it as absolutely brutal, both psychologically and physically to Supes.
If this were in the movie, it would have been more apparent why he was essentially stalking Lois. He felt he had absolutely no one as Superman - and he didn't. But that message didn't come across clearly. The people I saw it with did not pick up on that clearly. They thought Superman was just some love-struck stalker, not the isolated, devasted person he really was. There's a HUGE difference there.
Had the Krypton-visit scene been in the movie, it would have shown why he was so distraught, so alone, so driven to re-kindle with Lois, the one person who understood him as Superman and Kal-El and even Clark. Instead we get one stupid line "That place was a graveyard, I'm all that's left" to set up the entire loneliness thing?
Doesn't cut it, sorry.