Good to see a new mapper! Thanks for posting screenshots.
I agree with everything Bloughsburgh said.
It looks like a project with potential, but a couple more suggestions:
The proportions of the map seem a bit too large in a few places. Examples include the raised Quake sign on the floor in the third picture, the wall-mounted lights in the first, fifth and last picture, and the stained-glass windows in the first and fourth picture.
The raised Quake sign will probably make movement around that room a bit more annoying than it needs to be. It's not high enough to block line of sight, so it's bound to just impede player movement. If you lower it so it's just a couple of units high (and maybe turn it into a func_illusionary), it will probably look and play better. This goes for intricate floor details in general.
As for the stained glass windows in pictures 1 and 4: I would suggest letting the textures lead your brushwork a bit more. It looks like you've scaled up and stretched that texture to match your brushwork. Instead, maybe try creating brushes that match the scale of the textures. That way you'll end up with slightly better visual proportions.
Also think about what the textures represent. A raised stained-glass window that casts a shadow (picture 4) doesn't really make sense -- so either use a different texture for that kind of object, or make the stained-glass window flush with the wall, or recessed (sunk into the wall).
A related point: in pictures 2, 3 and 5, you've used a door texture that is rounded on top, yet you've placed the door brushes inside a rectangular opening. Here, again: let the textures lead your brushwork: if your door texture is rounded, turn the doorway into a corresponding arch. Or else, use a different texture for the door.
Also related to texturing: pay attention to all sides of brushes. The ceiling lights in pictures 3 and 5 have the same texture (the light texture) on all sides. That texture should only be on the bottom face of the brush; the sides should have a different metal texture.
The rooms themselves seem a little too large for the sparse detail they have: the ceilings are high, and the walls are pretty uniform from floor to ceiling. This tutorial might be helpful in learning to avoid that sort of thing:
http://isoterra.co.uk/quake/tut1/
I look forward to seeing the map develop further. :)