My showcase

[Slanderous]

It looks great as for your first level, man! Here are some tips I have:

Firstly, on the first two screenshots I can see that you used the torches. I think it's kinda odd to have them placed so highly, I'd suggest lowering them down a bit. I think the 1.75 height should be sufficient.

Second thing I want to mention is to toy around with particle systems and bilboards. With particles you're able to add dust and other stuff flying around, which would greatly improve the general look of your levels.

Lastly, be careful not to overuse decals; they take an irrational amount of space and can really boost your map's size. Also, HPL2 seems to sometimes have problems with rendering the decals, so once you've placed a decal and decided to move it, make sure to remove it and use the decal tool to place it again, as moving the decals might lead to the level editor's crash.