I think you miss a great deal of character development that is crucial to actually developing a sense of familiarity with the characters. Depending on how you felt about the ending, you may have either saved yourself more disappointment by not reading the other 3500 pages, but if you liked the ending, you probably kept yourself from feeling the closure that I came to feel once the characters' fates had been set by the ending.
This is the first series of books that I have ever read completely, and I must say that I enjoyed every bit of it.
Not reading one caused you to miss the best book of the series, and I mean the original, not the edited 2003 version. The original version of the first book was by far the best. You can literally feel the tension and mystery, and it leaves you gaping and trying to fill in the holes as you speed to the bookstore to buy the second.
King has stated in interviews that he plans on rewriting the entire Dark Tower series (what we have is a "first draft"). He also stated that when this rewrite occurs, he is considering writing himself out of the series.
That's an extremely interesting proclamation! Could you cite your source?? I'm interested to know how he'd do that - seems like it would make for some drastic plot changes, and a lot of edits - unless he just changes, "Stephen King" to "Richard Bachman" or something similar.