I think the Da Vinci Code is a cut-above most thriller fiction not in its plot complexity, certainly not in its character development, but in its perceived 'high-brow' topic and one which so many people have a view on i.e. religion.
There are better thriller writers (Ludlum for example) but the fact that so many of us have gone out and read his other books says a lot about how enjoyable his books are. For me, Da Vinci... and Angels and Demons were grat fun to read, no more than that really, while the other two were pants. But I still finished them.