Why can't there just be a Superman story and get on with it? It doesn't all have to be retold. Let's just have the basic elements of Superman without all the continuity. Like a Fleischer cartoon, there's no need to question it, they just get on with it.
The first Fleischer cartoon, (simply titled "Superman") did tell the origin, so I'm not sure that example helps your argument.
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Why does everyone assume that the origin is going to take 20-30 minutes? STM spent a lot of time on the pre-Superman stuff because the movie was written as a 3 act play and was 2.5 hours long! They had the time to tell it. Also, STM was just the first half of the Superman/Superman II "Mega Movie."
I say we need the origin, because that film WILL be someone's first exposure to Superman, just as STM was mine. Not everyone who sees these films is a comic fan. We also need to show that this is a separate story from what has come before. (Some people will always be confused ala Begins and TIH, but we need to try.)
That having been said, I don't think we need a linear origin, nor do I think everything needs to be laid out. We don't need a ton of background on Krypton, we don't need to spend a great deal of time in Smallville. We need only the information that tells the viewer who this person is, and why he does what he does. Tell the story ala Begins in flashbacks, etc.
We
can start with the ship crashing, we
can show some scenes in Smallville and we
can show his travels throughout the world and how his experiences in these places helped him decide to become Superman, and we can do all of this without revealing that he is from Krypton. He doesn't even need to know for sure if he's an alien. Look at the Smallville pilot and look at MOS. In Smallville they were pretty sure he was an alien, but they didn't know where he was from, and in MOS, they weren't even sure he was an alien. I agree that revealing the Krypton stuff in the second film, especially if it ties into a villain like Brainiac (the Kryptonian version or the Coluan, "thief of Kandor" version, either would work).
I would start with Krypton exploding and the ship flying through space and then dissolving from the ship to the bullet that shoots Clark's friend in Africa, just like in Birthright. As I've said many times, that section is about the only useful part of that story, and I think it suits a film very well.