Ive read most of the Dirk Pitt series. Cussler is a great author, but I never really saw the stories as anything more than cheap entertainment. I'm not surprised that Sahara was a flop because I've always kind of thought of the Dirk Pitt books as "B" movie material.
I always liked Raise the Titanic!, followed by Night Probe. I even have my autographed Clive Cussler photo here with me. Some of his later books can be on the ridiculous side -- too much Dirk Pitt derring-do/romance and not enough history -- but that's just my take.
In defense of Hollywood, no author is forced to sell the movie rights to his or her book. If you do, expect some major changes and omissions as you're venturing into a different medium where they simply can't translate the book word for word onto the silver screen. There's not enough time.