My wife and I, plus her parents, took a gondola ride at the Venetian and we had lots of fun. They're pretty up front about the duration of the trip (10 minutes).
We opted for the indoors ride, as the sun was baking on the day, and they told us that the ride doesn't pass through any shade. Rather than burn to a crisp, we went indoors where the ride passes through the 'streets' of Venice, and along to the square. It's quite cute, though don't expect anything spectacular. The gondoliers are really great, and make the ride a lot of fun. You get three songs for your money, and they all seem like good singers.
It's probably not great as a romantic ride, even in the evening when the faux streetlights are on, as the crowds and onlookers are always going to milling around. It's also not very private. However, we've not yet done the real thing in Venice, so we were thrilled to have a go, and it's all good fun.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.