The two biggest 'issues' I have with your map are how linear it is, and some of the texture choices.
It's natural that a first map will be very linear. I remember figuring out Doom Builder for the first time and just stringing rooms together one after another to try to make the map as big as I could.
This lends itself well to creating what amounts to a very long hallway filled with monsters. The problem is that linear experiences tend not to be very exciting if they aren't implemented effectively.
Let's look at the paths the player can take in your map, I've drawn a black line indicating the path the player "should" take, and a different colored line for alternate paths:
Spoiler:Compare that to the paths available to the player in Doom's E1M1, and Doom 2's Map01:
Spoiler:Just for fun, here's Plutonia's Map01:
Spoiler:Notice that your intended path is very similar to both E1M1 and Map01; they go from start to finish without crossing over themselves.
Where they differ is that E1M1 and Map01 have other areas the player can access, adding some depth to the maps.
E1M1 rewards the player with both green and blue armor for exploring, and Doom 2 gives the player some armor, a shotgun, and a rocket launcher.
Exploring these areas is not necessary to complete the level, they just add a bit of detail, and make it seem like you're in a run-down base rather than just a hallway.
I would experiment with making a map that forces the player to backtrack in order to progress.
For example, show the player a locked door early in the level that they must return to when they have the proper key.
Just don't get carried away; you can make a map that requires the player to run back and forth between two rooms pressing switches, but that wouldn't be fun either.
As for texture choice, it seems like you picked a few textures at random instead of coming up with a theme for the level.
That's not to say that changing theme partway through a level is bad, but it has to be done in a way that makes sense, otherwise it becomes jarring and ugly.
I also suggest using height changes when you change floor or ceiling textures:
Spoiler:Also, while some textures may look fine being repeated infinitely, this doesn't hold true for doors. When they say 128x128, they mean 128x128:
Spoiler:Overall, it's solid for a first map. The doors function properly, which is far more than I can say about my first maps.
As for your tightrope idea: Try playing around with 3D floors and sector action things.
You can implement your idea with a super simple script that gets activated when the player hits the floor.
Check the Wiki for info on ACS scripting.
I'll leave the rest up to you, and I hope you stick around and continue creating.
