I'd never looked at it quite like that, but yes, I see some very valid analysis there. I'm not sure that Ep4 is darker than 3 appears to be, however. For example, my kids can watch nearly all of Ep4 without freaking. Ep5 less so. The ewoks kind of freak them out, but that certainly doesn't make EP6 darker. Again with Ep1, there are large chunks the kids can watch. Most of what they can't has to do with action rather than darkness (i'm willign to put them through the pod race, though Kirsti isn't). Ep2, we haven't found much of suitable length to show them (perhaps the courting bits on Naboo, but that doesn't interest me. Perhaps it would the girls though). Ep3, well... from what I'm seeing, I have little hope they can show any. So while there is a general trend downward into darkness, I think it's interrupted, rather than continued with Ep4 (the destruction of the Death Star is a mighty blow for the rebellion). They take a step back up, but fall a bit again in 5.
It's well known that Lucas likes the Cambellian interpretation of myth, and tries to use it in his work. What's interesting is that he also uses a Medieval story telling technique. If you read Medieval literature, esp of a mythological nature (ie, Beowulf, Song of Roland, et al), the events are more important than the narrative voice and description. YOu are expected to fll in a lot of your own details. Lucas, intentionally or no, also leaves much of the personality/detail construciton to the viewer. His focus is on showing the events that together form a meaningful sequence of developments. I've found it to be very effective, however, it doesn't make the movies very accessible for casual viewing. The original trilogy managed to fuse both the casual viewing and the myth-cycle/story-telling aspects, which is why they are superior to the prequels thus far -- they're just better examples of filmmaking.
And, as many of you know I've argued before, the prequels are effective at treating a new take on the Faustian figure and the consequences of Faustian pursuits. In the series of well-articulated understandings of the Faust figure, I have to put Goethe first, naturally. Marlowe comes next, and then there are some French guys with some fairly weak ideas of Faust but some effective presentations of those ideas. Lucas is probably on this third level, with much better ideas about Faust but less-well articulated in terms of enjoyability.
There, we've effectively intellectualized your space opera for you. Hate us or love us for it.