I think it is way too early for me to stop at the Expert Mode. Somehow, the "Hardest" word in the Ultimate Block Puzzle really intrigues me. Then, "Challenge Accepted". But it isn't free. With less than $3, now you can play 1000 puzzles more.
Wondering how the puzzles look like? Here's the preview.
At first sight, the main difference is - having an additional block (11 now instead of 10 in the last level of Expert Mode). Most importantly, you can expect that, when the level goes on, it might grow more and more.
Are you guys playing this mode? Guess i would be posting the solutions soon. :)