Napa is to wine as Disneyland is to kids entertainment or Las Vegas is to adult entertainment. It's pretty overwheming with a winery about every 50 feet.
Personally, I prefer the Sonoma Valley (the next one over to the west). It's like the Napa Valley was maybe 15 years ago. You can still find some smaller, unspoiled wineries nestled in the vineyards where the winemaker is in the tasting room pouring the wine.
But either way, it helps to have a plan and know where you're going.