@karlknow - Guessing is never required. Each puzzle has one and only one solution, and each is solvable using only the clues given.
@deborah - We are looking into adding an option for players to select only puzzles of a particular difficulty level. It's hard to make that work within the confines of competitive play but we're working on it. That said, don't give up on the new puzzles just yet - most aren't that much harder, they just require new forms of deduction you may not yet be accustomed to.