Good.
That's quite complex to rate.
Graphics? Poor, 2/10.
Style? Old game style ... Well ... 5/10.
Sound? Nothing outstanding, match the graphics' depth (MIDI) ... but I didn't get bored of the music so 5/10.
Violence? Like it matters: 0/10.
Interactivity? Gameplay is simple but great: 9/10.
Humor? 4/10 (Only one joke inside but it made me really laugh)
Overall? Simple but addictive, levels get harder and harder and are well designed: 8/10.
Only one bug to report: To get the rune with the second character I felt on the ground at the very start (mistake at my first try), water went up but I was allowed to finish the level "swimming".
I reached the end and really liked the way you did it ;-)