9/10, 4/5. Got stuck on 20, Spent around 5 minutes on 18. A bit hard, and i got a headache after 10 minutes.
I thoroughly enjoyed that. It was new, unique, and pretty fun to play. But I only got to puzzle 24 because I have the attention span of a housefly. =P
It's really good and really hard (I got stuck on 27, which is bad compared to those of you who beat it) but I also add that you could've had more movements like a square or a diagonal movement. A level creator would be cool too.
For such a simple graphic, it is pretty nice: I spent an interesting hour beating the game.
About a sequel.
You could add "diagonal" levels, or any pattern you would (example: instead of a 4 elements straight line, a pattern like the horse movement in chess).
Also, a moving level would be quite amusing to see, altough I don't know what could be the outcome...
Finally, you could put a level creator, so that you could even get a whole new set of puzzles from users and add the best ones.
i dont know how you came up with this game but it was amazing it took me a hour to beat but it was a fun game.
level 50 took me 20 min. to beat