Minor recommendation - show a notice that more categories will be unlocked as you play. It might be confusing for new players otherwise. (It's not immediately what the 0/1 means.)
EDIT - Seems there's a bug. I completed the first Greek Gods wordsearch (the first category that requires 2 solves to progress), and the second puzzle was identical to the first. Exact same words to find, same letters layout, etc. I played through in 1 session from the start. After closing the tab and reopening, I chose Greek Gods again and got a new puzzle this time. If it matters, I'm using Firefox on Linux Mint.