It looks a bit grey, to be honest, but it comes across to me as a design choice on your part, so thats fair enough. The problem is that its grey with default HL textures, and those are some horrible textures :sad: You should perhaps experiment with some custom textures - check out the wadfather for a whole load of them...
http://www.planethalflife.com/wadfather
Something that doesn't do your map any favours is your lighting. It seems you have used very few sources, and all of them are the same colour. Having some variation in your lighting could do wonders I think - some small coloured lights here and there to break up the monotonous bright white could improve things greatly.
Architecturally, you have some interesting things in here, but a few things just negate them entirely. Namely - the stairs. As far as I'm concerned, those are not physically possible, no one stair is even attached to the next! Put a trim along the sides or something to hide this problem.
As I said, there are a few things of interest in here, for instance those pillars with the thin centre section. I'm assuming this is an early map of yours, in which case its nice to see you using some degree of variation rather than just make big blocks for everything.
I made a somewhat similar map to this not too long ago, called Seneca, which you might wanna check out for some ideas and inspiration. I used light_spots in that extensively to provide lots of contrast, and I think playing around with them could help out this map too. It can be found in my profile if you are interested :smile:
