Excellent value, with a good selection of stops around the city. The boat ride was relaxing and informative.The round-trip takes around 2 hours, so it can be difficult to stop more than (say) 3 times per day.
One caution ... the Viators voucher told us to go to a specified point to exchange for tickets. This was a taxi ride from our hotel. We later found that the tour operator had booths (yellow vans) and salespersons at numerous bus stops, se we (maybe) could have saved the cab fare. There was a bus stop close to our hotel.

Excellent. Enthusiastic and entertaining local guide/driver. Lots of information. Convenient pickup/drop off points. Other "tips" re what to do and see.

The tourist section of Quebec City is very compact and this bus tour will familiarise you with the layout. Thereafter, the main attractions are mostly walkable.

We were fortunate to have good warm and calm weather. We chose the large boat and saw Minky whales and hump backed whales (the ones that show their tail flippers as they submerge). There were planty of whale sightings (July 2012).

The commentary on the boat was enthusiastic and informative. It was a super experience.

The boat was confortable and spacious.

The bus trip from Quebec City was approx 3 hours each way (including a comfort break). The bus was comfortable and the driver/guide was entertaining.

Good points - hotel pickup/drop off, we saw most of the main city centre attractions, plus the olympic stadium and other outskirts sights.

Less good - the driver/guide did not seem particularly enthusiastic.

Excellent. We only had one day to do the hop on/hop off tour, which isn't enough. You need at least 2 days.

The tour enables you to get to around 10 attractions in the city centre and outskirts.

Our guide was Gilles - he was enthusiastic and informative. thank you Gilles.