I tried to manage my expectations for this, but it wasn't easy after waiting 25 years to see the movie as it was meant to be. OK, it was more like 20 since I knew that the Marlon Brando scenes existed -- Still, that's a long time to wait, and ya can't help but build it up over such a long period.
The result? Eh. Uneven.
Interesting experiment, certainly.
Donner had shot about 70% of Superman II when the Salkinds fired him (and Brando, and John Williams) to save money. Lester then came in and shot the other 30%, and reworked & reshot quite a bit of Donner's material, too (in the commentary, Donner and Mankiewicz speculate that Lester had to do a certain amount of reshooting on stuff he didn't even change just to be eligible for the director's credit).
So Donner's task was to go back, restore what was removed, and find a work-around for the stuff that was never shot. The result is inevitably choppy. Lots of things don't link up.
Superman The Movie was originally slated to end on a cliffhanger. The missile he hurls into space explodes, and that cracks the Phantom Zone, releasing Zod, et al., who head to Earth. (Not sure if that means Lois is dead when the second film opens--but I'd imagine not.)
Donner restores this and loses the Eiffel Tower sequence--which I ended up missing quite a bit. "Pulitzer--Capital P, little U," etc. It was a fun sequence, and a shame to lose it just 'cause it was shot by the other guy.
Lois figuring out Clark is You-Know-Who is also quite a bit different. The location shoot at Niagara Falls was entirely done by Lester. In Donner's version, Lois simply looks at a picture of Superman in the paper, then at Clark, draws a hat and glasses on the picture, and voila! She confronts him, and throws herself out the window of Perry's office.
Clark uses his powers covertly to protect his secret while ensuring she has a soft landing.
Instead of sticking to Lester's follow-up, which had Clark tripping over a bearskin rug into a fireplace without getting burned, Donner used Reeve's and Kidder's screen test footage.
Lois decides her mistake was putting herself in danger and suddenly she's got a gun pointed at Clark. "Don't bother falling down now, Superman, you'll just have to get back up." And she fires.
Gotcha! The glasses come off. The jig is up. But Supes is pissed: "if you were wrong, you could've killed Clark Kent."
So it was a clever workaround, even if it doesn't quite link up in terms of production values, and with the fact that the next time we see them, they're in the north pole, but whatever.
Then there are the legendary Brando scenes -- the only scenes he shot with Christopher Reeve (the scenes in the original were shot with Jeff East) -- and they *were* fantastic. So much more powerful than the reshot stuff with Susannah York.
In Lester's version, we don't actually see how Clark gets his powers back, only that he finds the green crystal. Here, there is one final, emotional scene with Jor-El, who tells Clark that this was the last contingency he planned for, to help his son rectify the most horrible mistake he could ever make: turning his back on his responsibility.
Then we come to the ending. *sigh* Donner says the turn-back-the-earth bit was never supposed to be used as the ending to the first one, so instead of the magic kiss that makes Lois forget, he turns the world back again. It's doubly ridiculous the second time -- especially because Donner keeps the scene where Clark returns to that little diner to settle the score with the trucker who beat him up. Of course, now the beat-down never occured. Presumably, Zod et al never escaped -- and now, Superman has a reset button he can use whenever things don't go his way. *blech*
So all in all, I prefer the Lester version -- which could've been vastly improved just by exchanging the Susannah York footage for the Brando stuff.