In Chengdu, I had a hotpot dinner that was the most spicy meal I ever ate. I have perhaps tasted food this spicy before, as for instance when cautiously dipping a chip in the extra-hot salsa in a renowned taqueria. It is very different consuming a full such meal. You know you are eating spicy food when you pour raw garlic on it to soften the flavor!
In general, the Chinese food has been a pleasant surprise. The variety is amazing. It shouldn't really be, given the size and the history of the country -- I think my perception has been colored by the limited experience at Chinese restaurants in the states.
One of many culinary delights: The famous Shanghai squirting dumplings. You cannot really tell they are squirting, except if you notice they are sagging with the liquid inside.
In contrast, the food in Vietnam was a disappointment. The best meals I had in Vietnam were French. Curiously, the main Gaelic influence there seems to be a slight over-representation of French restaurants, plus a few loaner-words.
I did have some really good hotpots, but even here, China has outshone Vietnam so far, both in variety and overall quality. Two problems with Vietnamese food is that you have to spice it up yourself - which can be tough with unfamiliar sauces and herbs - and the best places are often local hole-in-the-walls that don't have names or addresses. Also, they often change around, as they go in and out of business. Thus, for the best experience, you really need to go with a local.