Is there really a point to this...? *sigh* Someone go get the link to the old ezboard. You can actually see the development from talking about Crestfallen, to talking about the unnamed RM2K project, to E1 being released, then on the NEXT PAGE OF TOPICS, E2 being released, and on the NEXT PAGE, E3 AND 4 BEING RELEASED.
So, yes, the first four episodes were much faster. It's a shame a lot of the images on the old forums are all broken now, I'd like to know what the first things we were shown were. I know there was a map of Marna stretch and, from the comments people made about a broken image, it sounds like he showed the image of Rhue at the campsite in E1 - the one that was shown in E4 when Rhue was injected with the formula.
The actual reason the first four episodes were close together is because Lun had most of them pretty much near completion before he released E1 - that way, whatever people thought of the Way he would continue, having done so much of it. E5 and E6 have taken considerably longer, over a year each from the previous episode, since Lun has actually still had a lot of them to do, and beta testing has taken a long time.
I don't remember exactly when E5 came out, since I beta tested in something like February last year and I didn't care quite as much about the release (although I still played it when it came out, since there were a few changes). I think it was around April last year. Beta testing for E6 seems to be going slower than intended (at least wave 1). I was expecting this from the day of the announcement, though...

I'd guess E6 should be out by July.