Just downloaded this and played through the first map. Kudos!!
My hat goes off to anyone who seriously persues singleplayer mapping. Overall, I was very impressed with the quality and scope of this project (of course, I haven't finished it). From what I've seen, you are obviously putting alot of hard work into this, and the quality shows.
That said, there are some areas that could possibly use a little tightening up, focus wise; mainly the 'puzzle' spots. This, however, is one of the pinnacles of great level design, and something that takes ALOT of experience to master - pushing the player through the experience without allowing them to see the 'hand of god'...i.e. "button B doesn't work, because you haven't activated button A" kind of messages. These are the things that really impressed me with HL2 level design; the fact that I would end up doing exactly what the designer wanted me to do, without it feeling like a cow in a cattle chute.
One of my favorite puzzles was in Blue Shift. There was a door, with some dynamite charges wired to it. The wire that connected the trigger and the explosive was severed. To solve the puzzle, you had to push a metal barrel between the two ends of wire, making a connection, and blowing the door. The reason I liked that simple puzzle so much, was that it was
A. Simple.
B. All in one spot (no back tracking 5 rooms to find the switch),
C. Dramatic (got to see somethin a blooow'd up!)
Anyway, I look forward to finishing this and seeing what else you may be working on. Great job sofar!!