Why does this book get a bad rep?

I just finished The Gunslinger, and i loved it. I thought it was an amazing story with amazing characters. It had a great pace and I loved the ending. It is one of my favorite stephen king books I've ever read, if not my favorite.

I don't get how this book gets such a bad rep? I've always heard that you have to slog through this book to get to the rest of the dark tower series, and that it is the weakest book of the series. I've heard before it may be one of kings worst books. I just don't get it. It was such a good book.