I've been trying to play though all the levels recently. The second part of the Aquarius level on the second quest takes the award for Hardest Level I think, Water Rising, enemies Spawning from 3 directions. This is the ONLY level I have yet to beat on the second quest. I even tried Game Genie, and still can't beat it. Knock back factor plays the biggest role, Thank God for save states right now (In this case, purely for saving and coming back later) because I can take about 10 minutes of it before I have to stop.