Right *cracks knuckles* Let's see if I can address some of this.
Firstly, I'd like to see anyone get hit by a van, particularly as badly as King was, and breeze through it without any psychological effects. He suffered some pretty horrible injuries, especially with his hip. Plus, as a writer, this was probably a good cathartic outlet for him; also, the accident was apparently the moment that made him realise that he needed to finish the Dark Tower series, as it was a reminder that something like the incident could happen at any time and kill him off.
I've already whittered on about the ending (seeing as this is a thread about such) so I won't go over that again. It's here somewhere.
OK, so they don't "expel the evil" in the story completely...this time. The implication is that Roland, as the last remainder of a time when the White was still strong and the beams were in good working order, will have to keep repeating his journey until he learns from his mistakes -- to trust his ka-tet, to learn to love, to remember his fallen comrades and most importantly that it's the journey and not the end that counts (which we see him starting to do, which leads me to believe that this particular journey is nearing the end of the huge cycle of circles that he's performed...especially as he has the Horn of Eld with him at the end. There's a lot of hope at the end if one can spot it).
As to the easy death of the villians (I have to agree to a certain extent, Flagg is amazing and his death is rather quick). The thing that I always go on about with King is his verisimilitude (yes, among all the supernatural, fantastical stuff he writes) -- his characters are always deep, with broad backgrounds; these are not just your typical bad guys, dressed in black and stroking their facial hair maliciously. Sometimes it's not fesible to have a long, epic battle between the good and the evil. Sometimes other things can befall them, on both sides. Sometimes accidents happen (SPOILER Alice and the brick in Cell, anyone?).
I've forgotten too much about the details of the pregrency to be able to really comment on it, I'm afraid.
What particular examples of dues ex machina were there? Also, again, one needs to remember that the story is a circle, and thus Roland the rest are all going to eventually end up in the same place. Not in identical ways every time, as we know, as Roland continually has to keep doing things differently, but roughly so.
I don't think a comparison can really be made between Susan and Roland's romance and the one that Susannah and Eddie have. They came to be under very different circumstances and have a very different 'feel' to them. Susan and Roland's is a very brief, passionate and secret romance of two adolscents just discovering such. Susannah's and Eddie's a much more deep, getting-to-know-each-other, finding love and solace in this crazy adventure they've been thrown into kind of love. They are older and wiser -- they've both seen a lot of crap in the world before meeting one another.
I'm starting to waste away through hunger, so I'll have to leave this now. I'm not saying that The Dark Tower is completely flawless, and I have my complaints with some of the parts (the rosy, happy ending of Susannah, Eddie and Jake was just too un-Kingly for me) but I've tried to address some of the parts where my opinions seemed to have differed. And it's always good to see people talking about King books, be it in criticism or in ardent love or somewhere in between.
Making such a comparison to the plot of Harry Potter isn't really helpful, though. When one puts it like that, then the Dark Tower series would sound flawed. But the similar events in the series happens within context of it, and has reason behind it.