Whatever you do, don't get discouraged!
I've been tinkering with BUILD since I was about ten. I've had a good year or two to work on Cherenkov Station but it took about five years of experience in making mediocre maps. Wanna see? Go check out the Duke Repository map listings and browse my old maps; everything before FOS Station and Area 27. (But even the mediocre maps came after about five years of tinkering--some of my early scraps of levels are truly bad.) I didn't think Cherenkov was that great; the reviews have really surprised me. I had given up on trying to make an "everything" map--a really detailed extraordinarily designed map like those that Gambini tends to make nowadays--after getting discouraged at maps like Blown Fuses, and from then on I just started focusing on putting Duke back in his vanilla roots and trying to polish everything as much as I could.
I actually started doing the same thing you did with RCPD--making a map to test all the BUILD effects, but I never made it into a coherent map. It's always practice, practice, practice, pushing yourself, stretching yourself. After awhile it's less of a "what can I do to outdo my last map" and more of a "Well, I just want to have fun--what happens if I do this?" By that time (and you're nearing there, if you're not there already; I honestly can't judge a mapper's abilities worth beans but I think you're very close) you have the experience behind you that frees you to do whatever the heck you want, especially if you can also free yourself from worrying about what other people think.
When I fired up Parkade I knew it was going to be TROR-laden but I was still shocked when I saw the fire truck, the car, the parkade. What really sold it to me was the ledge with the glass windows in it. I saw that and thought, "No way! I just stepped into GoldSrc!" (My other favorite game engine.) I mean, *maybe* the ledges at the EDF base could've been faked with exceptional spritework. *Maybe.* But details like the skybridge with the hole in it amazed me.
What I really liked, though, were the "classical" elements of the map. The design of the rooms; the details like the posters and the signs; and especially the sector-based lighting when it existed. (I know--wall trouble. Curse you, wall count!!) The different sections flowed smoothly into one another; there weren't any disjointed sections. It's not a perfect map, just like Cherenkov isn't a perfect map and It Lives isn't a perfect map and Deadfall isn't a perfect map and all of the Last Reaction & Water Bases maps aren't perfect maps (sorry, Mikko!). But Parkade is an enjoyable map, and as a fellow mapper I can appreciate the effort you both put into it.
I haven't played the final yet, mind you; downloading on dialup is slooooow.
I'm basing my comments off the version I beta tested.
So, now that I've said that...
Why IS there napalm in the office?