Looking from the Japanese perspective, the biggest difference of Japanese and American TV ads is their time lengths. The average time length of an American TV ad is about 40 seconds. However, in Japan, the average time length of an TV ad is only about 15 seconds. It is very rare to see an ad that exceeds this time.
This difference directly affects the contents of ads in each country. In America, we see a lot of ads with short stories (or a skit, I guess). Below is my favorite example, which is the ad for Pepsi Max.
On the other hand, Japanese TV ads tend to use music to catch the audience's interest, as I mentioned in the post before. There are ads that use songs by famous artists, but there are also many ads that use original songs. Below is the Japanese snack TV ad.
Speaking of that, in Japan, we call these songs used in TV ads (regardless of whether its original or not) "CM song", meaning "commercial song". It is a popular way of grouping a song other than basing it on its genre, but it seems like I still have not hear the work in America yet.