The music was fine to start with but after 5 minutes of it the repetitiveness got to me. The gameplay had a bit more variety but was starting to become repetitive too by the end. That said, the level design held up well and was nicely graduated for increasing difficulty.
Not knowing where I was supposed to be going was frustrating. I just tried to get as far as I could without being seen, which seemed effective but I had no idea how far I was from the end of either the level or the game.