CONTAINS PLOT SPOILERS NECESSARY TO COMPARE/CONTRAST TWO VERSIONS
When considering the value of The Donner Cut, when compared to Superman II (Two-Disc Special Edition), two major issues arise:
Issue A: the controversial decisions behind the movie's production...i.e. the change of director, dissent among cast and crew, cutting Brando, script re-writes, etc.
Issue B: the end results of said decisions, which was initially the theatrical version but now includes this alternative...i.e. which movie tells which part of the story more effectively.
I see little sense in mixing these issues, since an objective view of the two versions (Issue B) becomes clouded when considering the facts (and speculations) of the movie's production (Issue A). In other words, I believe it is more important to look at the two movies for what they actually are, both strengths and weaknesses - NOT what anyone might claim 'could've been/should've been,' based on the differing accounts of the troubled production.
Full disclosure: I am an unapologetic fan of the theatrical release of "Superman II." I loved it as a kid, and I still consider it my favorite Superman movie to this day. Over the years, through repeat viewings, I have come to see some flaws in the storytelling but nothing that significantly altered my appreciation of the movie. Of course, I also became aware of the backstory of the making of the film and was intrigued by the personnel changes (key among them, of course, the firing of Donner).
I have to admit I was hesistant to even watch this so-called Donner Cut. There seems to be an awful lot of group-think regarding "Superman II." Many of the supposed flaws of the theatrical cut - often attributed to Richard Lester - have never made much sense to me. Along with the Salkinds, Lester has obviously become vilified as a bumbling hack by a large portion of the fanbase, while Donner has been elevated to something approaching visionary genious. An objective look at their filmographies reveals Lester as the more influential and distinguished filmmaker, while Donner is more a director-for-hire without any discernable style. Take that for what it's worth, as it doesn't necessarily make either director's vision of "Superman" more valid. I only mention it as a rebuttal for those who are under the impression that a 'great artist' was replaced by a 'talentless automaton.' If Richard Donner is, as seems to be a frequent claim, a great visionary - where in his catalog of films is this apparent (other than, arguably, "Superman: The Movie")?
Having listened to Donner's commentary on the Donner Cut, as well as the Salkind/Spengler commentary on the theatrical version, I see no reason to 'choose sides' over the change-in-directors decision. True, Donner did an excellent job with the first film and doesn't seem to be any apparent reason his sequel wouldn't have been excellent as well. True, Donner seems unwilling to admit any wrongdoing regarding his behavior and working relationships on the production. But it is just as true that the producers feel justified in the decision to replace him. The point is, we'll never know who was "right" - that type of 'truth' is usually so subjective that even the parties directly involved aren't necessarily right or wrong. Filmmaking is a collaborative business, and the money-men are going to say who continues to work on a given project and who does not. Maybe Donner was hell to work with, maybe he wasn't - we, the viewers, are not privy to what actually transpired. That is all part of the aforementioned Issue A...
...bringing me to Issue B: which version is better? The one clear benefit of the Donner Cut is the inclusion of the Brando scenes - it is stronger than the theatrical version's Susannah York scenes. I think that Kal-El interacting with Jor-El makes more sense in the context of the first film than having him talk to his mother. Seeing how Kal-El's powers are restored is better storytelling than having him simply reappear in Metropolis at full-strength, as he does in the thearical version. This is the biggest problem with the theatrical version. Of course, going back to Issue A momentarily, it should be understood that Richard Lester did not choose to remove Brando - the producers did. Why? Certainly not to sabotage Donner's work, but rather they were doing exactly what good producer's do: maximize profits. Paying Brando was going to cost millions of dollars, yet the producers realized that the movie's success was pretty much a given with or without him. But back to Issue B, finishing the Jor-El story arc makes more sense than having him MIA while Superman works things out with his mother. The strength of the Brando footage is the only clear-cut example of the Donner Cut trumping the theatrical cut.
That's largely because the Donner Cut is not a finished movie. There is a fairly considerable amount of Lester-directed footage still present, since the story couldn't be told without the inclusion of at least some of the theatrical cut. I happen to like seeing more of the villians in East Houston, Idaho - much of which has been edited out. I much prefer the Niagara Falls scenes - including Lois in the river, as well as the hand-in-the-fire reveal - to what is found in the Donner Cut. Why would I want to watch early test footage that looks like it came from an entirely different movie? Sure, there wasn't anything else available (for reasons pertaining to Issue A) but the bottom line is that it doesn't look good nor does it play well. Reeve and Kidder hadn't fully arrived at their characterizations as would be seen in the actual movie. From a visual standpoint, it is perfunctorily staged (at best) as it wasn't meant to be included in a final movie. The theatrical version, on the other hand, presents a much better realized scene. And I know I'm skipping around at this point, but losing the Eiffel Tower sequence is shows a major weakness in the original conception. Freeing the villians as a result of the bomb from the first movie isn't exciting - we're watching rehashed flashback footage from the first film as the villians are released. The theatrical version presents an entirely reimagined - and infinitely more engaging - set of circumstances that allows us to see Superman in action much earlier in the film, while providing the same reason for the villians' release.
As explained in the supplementary materials, Superman turning back time was originally planned as the ending for "Superman II." It was used, of course, as the ending of "Superman: The Movie" - so re-using it in the Donner Cut is simply a way inserting something because no ending had been conceived by Donner and Co. There's no ending to the Donner Cut because the "ending" we see would have never been used even if Donner had been allowed to finish the movie. There's no reason to even speculate how Donner's finished "Superman II" would have ended, since it has never existed. Watching the Donner Cut - even as a stand-alone movie - results in terrible disappointment, because turning back time to the very beginning of the movie renders everything we just watched meaningless. It's a variation on the old grade school creative writing cliche "it was all just a dream." In order to make Lois forget that Clark is Superman, the clock is turned back and the whole story we watched was erased. It's a cheat, and it's simply bad storytelling. It also underlines in bold-face that what we have watched is merely a collection of alternate scenes strung together with segments from an actual finished film spliced in to approximate the experience of watching a full movie. The alternate footage is interesting, but ultimately doesn't come close to supplanting the theatrical release.