Our tour visited 3 wineries: Madonna, Sutter and Andretti. Madonna gave a great basic introduction to wine tasting. Sutter has truly beautiful gardens that are well worth a visit in their own right, and have some nice crowd-pleaser wines. Andretti gave excellent, in-depth information about the Napa region and wine growing in general, and they have a lovely courtyard where you can sip wine overlooking the vineyards.
Our tour guide/bus driver was friendly and informative, if a little over-talkative.
The whole tour ran at a relaxed pace. The leisurely lunch break in Yountville was excellent. (Lunch itself wasn't included, but Yountville has an array of excellent options at different price points).
We particularly appreciated Tower Tours flexibility in letting us stay overnight. Technically this is a one day tour, but they were happy to leave us at Napa at the end of one day, and tag along on the following day's tour bus to get home at the end of the next day.
If you are a wine connoisseur, you may want to choose a tour that visits some of the more sophisticated wineries. But if you want a relaxed tour of the valley, interspersed with some nice easy-drinkers, this is the tour for you.