Great game!
I'll preface this by saying I'm not a cryptography expert by any means. I actually missed the first puzzle because I miss spelled the answer.
I like the overall design and the idea is pretty neat. Once I got into it, it was fun scouting around the site, trying to work out each of the codes. Though I will admit, I ended up using trial and error on the third number because the cryptogram with the grid of letters went over my head. Again that might just be me. But I got the other three and that gave me a lot of satisfaction.
If I had to suggest one thing, it would probably be to make the game full screen. In the pig pen puzzle, it was a little tricky to distinguish between a blank pen and a pen with a dot.
Overall, interesting game, interesting mechanic and I it would be interesting to see how this game and mechanic continues in the future.