I'm reading Dune right now after having avoided reading it for years. It's fantastic. I can see what all the buzz has been about, and I find myself constantly thinking that this is where Warhammer 40K got some of its inspiration back in the day.
As for The Dark Tower... man, I lost steam with that one. I read either 4 or 5 of the books, I can't remember, and 4 (that was the one in the past with the small town, right?) was just amazingly good. It was a shame that it was more or less bookended by complete bullshit. I can't remember if it was the end of 4 or 5 (I think 4) that sucked so badly, but it just completely and utterly killed any desire I had to continue. The whole "Wizard of Oz" thing. So utterly fucking stupid. Any lesser author would have had that shit rubbed in their faces to howls of laughter and been shown the door. I suspect that things improved from there and that it was just a particularly jarring turn of events that might have eventually made a little more sense or given way to something better, but I just couldn't make myself want to read anymore after that. Most idiotic way to end a book ever.
Still, I greatly enjoyed 90% of what I read before that, with a few caveats. It was a good yarn, and I hope someday to see it through to the end just to see what happens.