Alright. One, welcome!
Two, the city is actually VERY good, it's got interesting features, etc. The only thing that "bothers" (largely my own opinion) me about it are the side roads. They look silly, just draw them out like the main roads, except using a smaller brush. Tedious? Maybe. Good results? most definitely!
Third, attachments, learn that shiznit! This forum is one of the few that allow you to upload your precious images directly from your PC!!! and holy bejoly it's a lot better than photobucket! (which is what I used to use.)
Fourth, aside from point two, there ARE other criticisms to give, but I believe people should develop their own style and don't really want to influence you TOO much. So I won't give them! On the whole however, an excellent first map, especially considering GIMP which you implied you may not have the most experience with, although you'll find it to be VERY versatile (except for large file sizes sometimes D.
EDIT: almost forgot to mention: for future reference, if you intend to continue to work on the map, it's usually best placed in 'Mapmaking Discussion & Philosophy' subforum area thing. One 'cause it ain't finished, and two, 'cause it'll prolly get more view there!