I enjoyed the game, despite getting stuck on level 3. For a fair few of the questions I would be going 'OMG THATS THE DIFFERENCE' as soon as the timer ran out. It was a nice game, but I didn't really feel enthralled enough to start over and try again.
Overall I would give this game an 8, mainly because it didn't draw me back to it. I can't pick out what it was that didn't excite me enough to want to restart, so I can't really advice you :(
As for the previous reviewer, I believe it might change every time you do the 'Spot the difference', but when it was my turn, I clicked on the hand (Bottom right corner, holding the cola).
Keep up the excellent work, I hope to play more of your submissions soon :D