No, really, don't be sad! Not all the hope is lost for you.
Noone ever made a perfect first map... at least there are not many who did this... and there are people who made and presented even worse first maps than yours... at least i think so..
For a map, you gotta take your time. You gotta do some brainstorming. Then you might maybe want to write down good ideas when they come, so you won't forget them later.
After that you can maybe think about what your map will look like and plan it somehow, then you can build it.
-> What DaMaN already said: Textures - you have to choose well and see what looks good and what does not.
Detailed brushwork might also add to the feeling and the ambience of a map. Don't forget to use func_detail here for small and/or angular brushes or the performance will suck and the compile will take a lot of time.
Lights: you have to put lights in every map. you can create a lot of different ambiences by just playing with lights and their different settings. Don't just drop white lights without any visible light source in your maps.
Which leads us to props: use the different prop_* entities to place models in your maps (like lamps and crates). This will look good and make your map appear less vast and empty. also it is better for the style and performance of your map than making things like lamps or trucks (or helis like in helicave) out of brushes.
That's what came in my mind right now and what i thought would help you...
But you can always add me in steam friends and ask me if you have any questions concerning mapping, modelling or whatever
