I'm one of those who started out doing Sudoku in the daily paper and easily bored of it. Kakuro is the next progression up, where you actually have to count. Like Sudoku, there's a great deal of logic involved, and you won't really gain competence until you figure out the unique combinations. (Like a sum of 23 with 3 digits has to be a 6-8-9. A sum of 11 with 4 digits has to be 1-2-3-5.)
This book is at a level of challenge that appeals to me. There are a few that a pretty simple (toooo soft), a few that are darn challenging (tooo hard), but most are in that wonderful just right. My only complaint about the book is that outside of the first few puzzles, they use the same grid. I'd like to shake it up a bit ... some more squarish than rectangular. I know, I know. Those don't fit well into rectangular books.
I just started Brown Belt and so far so good!