I often get asked this question by people who are interested in why I keep taking Rick Steves tours. I like the fellow tour members and getting to know them and staying in the center of the historic parts of the cities. But the main reason is that the RS tours utilize all five of your senses. Let me explain, all tours use vision as the main sense in your trip, for many they are loaded on buses and driven around a city with someone pointing out the key sites, you might stop and someone with a flag on a stick takes you through a museum,etc, but it is mostly just seeing things of interest.
I have found that on the RS tours they like to involve all five senses, the group dinners are usually in non-tourist restaurants, so you taste what the local cuisine is really like. You get to take a cooking class on most every trip that also brings taste into the experience. When we were in Scotland we went to a sheep dog demonstration and as we sat on the rocks watching the dogs work the sheep, one came over and sat next to my wife and she petted and interacted with him the whole time., touch is a powerful experience. While on the Sicily tour we were invited into the home of a Countess and at one point sang for us (she had been a opera singer), while in Tuscany a local farmer had us operate a machine that shakes olives out of the tree to be harvested. While in Switzerland we visited a family home in the high meadows and helped make cheese, the smell of that experience was a mixture of the heating of the milk vs the cows and milking them.
So, in conclusion, I think that the reason I enjoy taking the RS tours is that they work hard to involve all five of my senses and for me that makes the trips exceptional experiences.