I actually I think there's just as many games in each column as before. The difference between this and Rhythm Heaven DS is that RTDS has 5 unique "worlds" + 5 worlds with harder versions of each game. RTW on the other hand has 7 unique worlds + 3 harder worlds. This was kinda disappointing to me, since I expected every game to have harder versions. I thought there would be 14 worlds, not just 10.
This is my main gripe with the game: between that and the little amount of extra games (especially the anemic 2-player content), it feels like the developers phoned it in at times. Some of the 2-player games aren't even that clever because they're absolutely identical to their 1-player equivalents. Maybe I'm just oldschool, but when I go from handheld to home, I expect more content (say, 100 main games instead of 50) and care. I don't like it when it feels like Nintendo's teasing or going experimental. If you're not gonna go all the way with one mode, don't bother creating it in the first place.