I enjoyed the first two simply because I sometimes like fast-paced adventure and trivia as an escapist sort of thing. Brown isn't a great writer, but he's not horrible.
I finished #3 a few days ago and honestly I was very disappointed. It was too simple and too easily figured out, no complexities. I too found that instead of wanting to read right through, I kept setting it down and leaving it.
I know that the the Lost Symbol by Dan Brown is a sequel to the DA Vince Code, but i just bought the lost symbol and i really want to read it. Will I not be able to understand without first reading the DA Vince Code?
I think you'll be okay. There are a couple references to The Da Vinci Code, but none of them had anything to do with the plot of The Lost Symbol.
I had to choke it down to finish it. It took longer to read the last chapter than the rest of the book. I gave it to my aunt and told her to donate it to Goodwill when she was done. This book sucked to no end.