Several friends told me to avoid Castello when we visited Napa. My wife is in love with medieval architecture and culture so I had to ignore their statements and go here. This place was the busiest we visited, lots of tourists here. The tour was expensive, $33 per person including a tasting of 5 wines. The tour was very interesting and the owner has definitely spent a lot of time and money doing it right.
However, that same energy and devotion is not going into his wine. We ended up tasting 12 wines and were not impressed at all. His reds are just awful... I would never buy them. The whites were ok, but overly sweet. Most of the wines on the list are German sweet / desert wines and were overdone. They smelled like a fruit bowl but tasted so sweet it hurt our teeth... seriously!
If you want to experience the tour which is extensive, and includes a torture chamber, armory and the gorgeous cellar aging area, then do it! But once they start pouring the wine... save yourself an hour and go up the street to Chateau Montelena or to Sterling.