Well mainly it would have to be the people, the music, the historic buildings.
Example: chambermaids at Hotel Sevilla make animal shapes out of towels and leave handwritten notes to guests, welcoming them to the hotel.
The people who deal with tourists display no envy, no resentment at all that these yumas get to enjoy life in a way that's denied to them. Even when they are asking you for something, they are keen for you to take something from them. A woman in Santiago begged me quite insistently for clothes of my five-year old daughter's, who she said was the same age as her own daughter (L). But by then I'd given away half of what we brought to give away and the rest was all promised. I'd asked L if I could give away her dresses and promised to buy her more in the UK, but L wouldn't hear of it. She's very attached to her clothes and I wasn't going to upset her - she wouldn't understand the argument of need. So I told this woman 'sorry, but no'. "Please," she said. "Or you give me something of yours," she said, "and I'll give you something of mine."
We were given salsa CDs, books in Spanish, necklaces made of seeds and beads, pottery ash-trays, little wooden dolls. Nobody took a thing from us without giving us something in return. The couple we befriended in Havana, Alicia and Giovannis, were desperate to take us to Coppelia, Cuba's favourite ice-cream chain (3 flavours!), where they insisted they'd pay for all of us (tourist money isn't allowed there).
Hotel staff, people in the street, everyone treats visitors well. It's a contrast with Mexico, for example, where tourists are also very important, but won't feel all that special.
Then there's the music.
It's incomparable and ubiquitous. Any band wandering the street is better than any so-called 'Cuban band' I've seen in most places, except top-notch Cuban restaurants in London and Mexico City. They'll play any Cuban tune you can name. In Santiago we asked for 'Donde Vas Domitila?' (the song played by the trio which follows Ralph Richardson everywhere in 'Our Man in Havana'). Well, those old geezers had never had the song requested, but they made a fair pass at it, improvising words for the verses.
It's awe-inspiring, such talent. Yulieski, the chisel-featured Santiaguero, a young salsa singer-in-training was the only uniformly cheerful Cuban we had dealings with. It was pretty obvious that he had music running through his head the whole time.
And then there's the gorgeous legacy of the Spanish - similar in grandeur to what you find in Mexico, but in the Oriente it also has a French twist that makes it all a bit New Orleans.