Whats your specs?

I found this with the VFR England scenery. It's because the sceneries are meant more for VFR in light aircraft than heavier ones. It might be taking a while to load if you have extended terrain textures checked (check your display settings). However, if you uncheck this, if you fly at high altitudes, you'll see an unsightly edge to the textures before the horizon. Thats why they're meant more for GA and low-ish altitude flying. In the same way, you might also find that, if you fly fast, textures don't load fast enough to keep up and get all blurred (again, best for GA aircraft), that might be why your city textures look bad. Otherwise, you might want to check your settings, make sure any texture settings are at full. You might also want to go into your CFG and try fiddling there to get good settings. There is a post on the avsim forums (I think) on how you can get your photographic scenery to work well with decent textures (you might have to search for England VFR).
Hope that helps,
Adam.