Well this feels weird -- about to say bad things about the author I've been obsessed with for years, and good things about the one I've been complaining about for the last few months
Regarding the Dark Tower, you've passed my high point of the series now. But that's because the first half of Waste Lands is some of my favourite storying of all time. I just love the parallel madness of Roland and Jake. And of course, the ruddy great Bear.
And I'd say that you've stopped just as the meaning's started to kick in. Now that the ka-tet is altogether, now the story really begins. And as to an un-established world -- yeah, that's largely what the Dark Tower is about. The world is fraying and and the Beams are failing. Plus it's not just about that world, but many. Many levels of the Tower.
As said, the next book is a diversion but you might enjoy it more because it does get more into Roland's world and where he's come from.
Books 5, 6 and 7 suffer from what all later King book suffer from -- King's runaway manner with his writing.
However, you should continue because it's King and it's a great series and because I say so
And yes, I have now finished all three feet of WoT (in all seriousness, I did have to somehow clear as entire shelf for this series...and maybe it is close to three feet...). I'll move over to the Jordan section to properly write about it but I will say two things:
1. The last three books were awesome awesomeness.
2. Leisha's right -- about lots of things regarding WoT, which I'll mentioned elsewhere, but yes, book two needs to be read. In fact I'd say it's the end of book 3 where you really start to appreciate the sheer scope of the series.