I actually liked Angels & Demons (the book) better than The Da Vinci Code, but it's the other way around with the movies. The Lost Symbol...I wouldn't exactly call it disappointing, since my expectations weren't that high, but it was pretty much a big 'meh' for me.
I think the movies, in the order they were produced likely added to the punch they had considering the Da Vinci Code is the one that gave him worldwide attention. But yeah, while I liked the A&D movie, you're right that the Da Vinci Code was the better movie. It was executed in a better manner.
I think the problem with The Lost Symbol is that it's ultimately unsatisfying. Dan Brown is not a great writer, and he seemed lost writing this. The concept was sound, and it could have been so much better if a better writer had undertaken it. As it is, it just fizzled.