First off, I think it's cool to see you venturing into parkour map building. Now for the critique.
The theme is original as there are no sewer maps other than Sewer Clown (Expert) which is a vastly different map. The build is accurate to theme, however it's a little boring. Builds like this are hard to execute due to the multiple level setting. On the outside, it looks like a bunch of floating stone brick boxes which is never what we want as map makers. You want to mask the surroundings and make it feel like a believable sewer. Shinx did something like this with his insane map Celestial Resort. A huge mountain to mask the room like structure of his build. The parkour isn't the best, but this isn't a problem. Parkour maps are now required to have jump variation so the map doesn't become repetitive and unenjoyable. Some of the earlier jumps on your map are a stream of head hitters and you also have a 3+1 as the first jump. Later on, there is and a x-facing double neo. These jumps do not fit the easy difficulty. Quick explanation on facing for you: X-Facing extends the corner of the block for a neo, aka you hit the block before you do on your screen. It makes a jump harder because you cannot just shift around and jump like you could for a z-facing neo. Z-Facing has no extension. For an easy course, 54 jumps is quite long.
For jump variation: I recommend mixing in weird blocks like piston heads, fences, beds, doors, trapdoors, cocoa beans, heads, anvils, enchanting tables, cakes, walls, you get the point
Also, you have potential as a map maker. Please don't hesitate to ask me any questions in game if you decide to make another map. my IGN is caseyclosed and you can always shoot me a message on discord if you have questions - casey#5392
