I agree, the money is falling on Singer's shoulders. Whoever said that this movie doesn't have the potential for drawing in people that want to watch it again is the nail in the coffin. Look at Batman Begins, it resurrected itself from a franchise that had doomed itself with bad movies, and exploded in DVD sales afterwards. You just like watching that movie.
Look at how we get to the first spectacle, or first peak of action in Batman Begins versus Superman Returns.
In Batman, you get the murder up front, a nice shocking moment. The scenes after that are like alternating touching moment and moments of angst, as Bruce remembers his parents, and is poked into being Batman, until finally his training is complete and we have a big action sequence.
In SR, we start off with Luthor getting an old widow to sign some papers, a crashed ship, some staring-into-the-corn-fields moments, some bungling at the office, and then finally we get to see Superman save the day with the airplane. By that point, were you thinking like 'for a semi-sequel, it sure takes him a long time to be Superman in this movie?!'.
The pacing just seemed off -- what should have been short and sweet moments, were long and border-line boring. The moments of action were either too short, or showed too much of superman-in-transit (which flying is nice), but not enough of things like when he detaches the plains, or lifts stuff. All of those intricate action moments felt rushed.
Finally, we could have gone with less stare-at-lois moments. Again, we need to relate to superman on a level, but remembering being desperate in love or acting borderline-creep against the unattainable girl does not foster good feelings. BB's romance wasn't much better (I think of it non existant since Bruce wasn't looking to be with Rachel), but you get a feeling that Bruce cares about the people around him and is emotionally engaged.
The SR luthor plot is forgiveable even, after all most superhero villians have pretty bad or simplistic plots. The green goblin had a crazy revenge plot, which was just simple. Doc Oc's plot was kinda stupid - kill everyone, and yourself for a science project. The X-Men series plots were nothing to write home about. Luckily, BB had a great villian plot that supported three characters (batman, ras, and scare crow).
I think we also came to expect more from Lex. Let's face it, the original Hackman Lex was much like the Spacey Lex -- diabolical, but not really logical (detonating nukes that would radiate your great real estate? It's just as bad as having a cold alien world for new real estate). However the Lex on Smallvile and Superman TAS have both been great characters, tactical, diabolical, and very logical in terms of their motivation. The Lex in Smallville is very believable about his plots and you understand why he does it.
It's the last set of scenes in Superman Returns that really drives my point home. The action in Metropolis is short and never resolved or fully realized (certainly the city would have more problems), giving way to Superman getting nearly dying from lifting something with kryptonite in it and then being in the hospital for a long time. I think audiences would have accepted some plot twists around the love triangle of Lois, but you don't want to see the man of steel looking like joe shmoe in a hospital bed.
And last, but not least - the son-of-superman. Perhaps an interesting sequel plot item, but it turned into its own little drama at the end with a speech by superman that appeared out of character and completely unmotivated.
