There's a dedication to Chris Reeve at the beginning. To be expected, but still nice to see.
The opening of the movie (before the credits) is mostly made up of scenes from the first film, but with new shots and dialogue scattered throughout.
The film opens with Zod's trial on Krypton, with nothing changed that I noticed. Not until the Phantom Zone disc appears, where we see some extended and slightly disturbing shots of the criminals' bodies being twisted around and stretched out inside the Zone.
We see baby Kal's trip through space juxtaposed with the P-Zone disc drifting aimlessly. At one point the disc actually seems to split into three, before ultimately merging again into one. There's some new Brando voiceover heard within the ship, specifically mentioning Kal's red, yellow, and blue blankets. We also see the spaceship crash-landing and opening up from a new angle.
Various more scenes from the first movie, ending with Superman catching Lex Luthor's missile and throwing it into space. My guess is that this is the second missile (the one that killed Lois before Superman went back in time), although it looked to me to be the same footage from the first movie of him catching the first missile (whew!). Well, whatever, hopefully it'll make more sense when there's time to sit back and enjoy it. Anyway, it's this missile that collides with the Phantom Zone prison and destroys it. No French terrorist plot here. The criminals are freed and Zod flies toward the camera, bellowing, "FREE!"
Cue the credit sequence, which is entirely redone to looks just like the opening credits of the first film. The genuine Williams score plays over it, not the weird synthesized version of it that was there previously. Brando's name is of course added (with Chris getting top-billing this time), and it ends on Donner's sole director's credit.
Next is the footage that was apparently shown in San Diego, with Perry congratulating Lois for her story on Luthor's imprisonment. Then Clark walks in, lovably bumbling as ever, and it gave me such a thrill to see basically "new" Chris Reeve footage. What follows is a pretty funny scene with Lois, pen in hand, looking back and forth between Clark and the picture of Superman in the paper. Genius reporter Lane draws little glasses on the picture of Superman and, guess what: secret's out. Easy as that.
Perry White sends Lois and Clark on the honeymoon hotel scam story, and all the while Lois teases Clark about the fact that she's figured it out. She's SO sure, she leaps out of Perry's office window. Clark runs down to the street faster than the eye can see, keeps Lois afloat with super-breath, then knocks down a sidewalk cover to bounce her none-too-gently into a fruit stand. Thatll show the bitch.
Lois' suspicions are later confirmed when Superman saves the child at Niagra Falls, leading to the scene where she proves Clark is Superman. Anyone who's seen the screen tests on the first Superman DVD will recognize this, and it's a lot funnier and cuter than the "hand in the fire" thing. Unfortunately, they're unable to HIDE the fact that it's screen test footage. It looks like a Clark Kent from five in the past has walked into the room.
I skipped over much of the middle and didn't see anything new until Brando reappears. Basically, holographic Jor-el takes the place of holographic Lara. I did notice that at least some of the "Zod vs. rednecks" scene is there, but hopefully not more than is necessary.
People will likely be glad to hear the "super-kiss" is gone. They'll likely be less glad to hear how Superman makes Lois forget: he flys around the Earth to turn back time. Yeeeeees, again. This actually serves two purposes. Besides making Lois forget, it also deposits the Kryptonians right back in the Phantom Zone. Truth be told, I'd almost prefer the super kiss. The time travel stunt worked for me in the first movie because he was THAT determined to save Lois, and it led to him rejecting Jor-el's teachings for Jonathan's. Here, it just seems like business as usual.
I didn't watch much after that, but there is a final scene in the Daily Planet, different from the goofy orange-juice-squeezing scene.