Looks like a really good start, my thoughts/suggestions (trying not to repeat mearrin):

a. The overall orientation of buildings (with some exceptions) is NSEW which makes the city look a little bit artificial (but that may be intentional, many cities are built on grid systems).
b. The major road pattern looks great, but the minor roads in many places look 'off' in the sense that they don't really follow a coherent pattern. The ones in Old Town look the best.
c. There is a kind of weird optical effect with the minor roads - it looks like you've bevelled a block and then drawn the minor road on top of the roof rather than the minor road 'cutting through' the block.
d. The roads outside the city are pretty jaggy - can you smooth them off a bit?
e. To my eye (and it's a very subjective thing) the level of detail and drawing style between the city buildings and major buildings make for a consistency clash.

Overall it's looking good though!