Great level! I found the concept very original.
I only found two parts frustrating: the part where you had to climb up the upside down pyramid thing (while I admit the jumps were not hard, I usually have trouble making 5 or 6 in a row without a break in between) and more so the umbrella jumps towards the end (for the blue key I think). The first jump wasn't too bad but the second took me a couple of tries.
Also, there was a very easy wallswim/void that you could use to bypass the keys and locks altogether. Simply enter the tunnel with the first (red) lock, and then step back out. Wallswim!