Alright. Most of these, the concrete especially, are pretty good for just starting, but I must give some tips.
1. Effective quantity is the soul of good texture packaging. Don't put in eighty thousand tiny variations of textures, especially when they are 256x256; keep texture memory limits in mind.
2. Don't use a big texture for what could be done in a small one. You could easily put those bricks or concrete tiles into a 32x32 texture, even 16x16; though this has definite implications about the amount of detail you put in these textures, keep this in mind for future ones. More importantly, never waste space, especially with a texture that is going to take up a lot of space, especially a vertical, in-your-face wall. Put grunge or at least detail into the bricks, put flaws in the tiles. And please, make 'darkglu' an actual material; as far as I can tell, currently it is flat dark gray with noise.
3. 'Bordering' areas of your texture - that is, making them stand out clearly by way of contrast, outline, etc. - should become your best friend. Because we're working with such small resolutions as Half-Life offers, any attempt for total realism should be abandoned; by making textures have unrealistically dramatic lighting and emphasis, it looks better than sacrificing detail for 'realism'.
4. Make your materials look accurate; you've used an almost identical base for both metal and concrete.
5. Color, dodge, burn, and photograph bases are your friends. To be perfectly honest, there is nothing exciting about these textures. No matter what some fools say, there is no grand skill and nobility in making scratch photoshop textures. Don't limit yourself.