Fantastic! I really love ambitiously crowded city maps. I agree with feanaaro that thinner lines for the buildings would probably look better. I would also suggest giving your monochrome areas a little texture, either with mottled colour or even just a very transparent overlay of a bump map or clouds filter (if you're using Photoshop) or something similar. Perhaps also a cobblestone texture for the city areas.

Also I notice that a lot of your back alleys are very straight. This may be one of those foundational changes that's not really worth spending time on, but if it's not a lot of work (depending on how you've built this map) I would suggest making the lines of the back alleys a bit more organic.

Ultimately even if you don't change it one bit from here you've got a great, detailed city map that is going to offer a fantastic place to explore. Nicely done!

cheers,
Meshon