Hi Dakkiller,
don't be too disheartened by the criticism you've received of your first level. You're obviously a novice at building Duke levels, but so was everyone here at one point, and your first level is the kind of map that everyone makes as their first effort. My first map was truly miserable. It's probably best to think of Strip Hotel as a training run, because the truth is it's pretty bad for a serious release.
You're getting the effects, like doors and water teleports, to work which is a good start. Now you just need to work on developing an eye for detail and shading. Look at real rooms and structures around you and start thinking, "How would I build this in Duke?". Also, work to a plan. It's obvious when a map author has not got a coherent picture of how the level is supposed to go, because they just put in whatever comes to mind wherever they want.
Good luck, and welcome aboard. We need more mappers around here, so don't let the reception to your first attempt get you down. You'll find you'll improve rapidly with more practice.