Yeah, it looks like the same game but with "American-style" crosswords (ie. far fewer black boxes than a "British-style" crossword), whereas the Sun one has British-style crosswords with both quick and cryptic clues.
I've only played the first four puzzles, but so far it's harder that CrossworDS (which isn't saying much) and easier that NYT. But I'm sure the difficulty ramps up as you proceed
By the way, can anyone tell me when Hiiro no Kakera DS comes out?