Some feedback from me...

Make sure you put in some more terms for the groups. I typed in backwards, world cup, languages and countries and didn't give me any!

To which you might argue, countries is too vague... Well because there are no other countries on there it's impossible to go even further to mention the 'christianity symbols on flags'. Technically countries is right too.

Which brings on to my main point - there needs to be crossover (some answers that could fall in to different categories). There are 4 names on there that are backwards so i clicked them without even reading them. There are 4 countries so there was my next guess. And then 4 first names so that was group 3. I had all 4 groups sorted in less than 20 seconds and that was with barely even reading them.

However, there are some really interesting groups there but it's just not difficult at all.. Need to throw in some curveballs! Cheers.