The first can be a struggle, its more gritty, you can tell it was written long before the rest of the series. That being said, I felt it really established Roland, so if your going to read any of the books, read the first. I loved the series and although it might not have ended as we'd imagined it, the ending fit with our main character, it's his story through and through.
Now the recent "addition" Through the Keyhole? Not a fan.