My apologies ahead of time if I duplicate advice given by others, especially mike (who is renowned for star trek)...errr... or star something. hehe.. sorry mike.
1. scale. Ensure everything is correctly scaled. The curb looks like it's over a foot high.
2. Materials. All materials should look like what they are supposed to be. Again, the curb, it looks like grey plastic. Remember the three main facets of a texture, color, roughness and bump. If you get at least these aspects it will help. You also need to use real-world references, for example find a photograph of a street in the rough area of the world where this building is supposed to be located in, and try to replicate what you see. Note that smoothing looks to be off. Every little oversight like that is a small CG signpost. "look at me, I'm artificial"
3. The George Lucas effect. Nothing in the real world is perfect. Without variation in size, shape and texture it screams 'artificiality'. Again, the curb jumps out. it's straight as a razor. They are NEVER like that, even when freshly poured. There would be natural curves and dips, not to mention a rain gutter, etc. etc. When you tackle a wide large scale image like this you need to be prepared to create LOADS of detail either via geometry or texture (usually a combination of both)
It looks to me that your modelling skills are great, but I suggest you start smaller. This is an enormous undertaking and unless there is a client at the other end of this image I suggest starting with a modest still life. Cutting your teeth on hyperrealism on a scene of this magnitude is really daunting. Personally I started with spheres and cubes then moved to things like TEAPOTS... then eventually to cars and shavers...
Seriously, it sounds to me like you don't grasp the enormity of your task. This is no easy fix, like what colors do I use to make it look like Mike's work. Mike's work looks the way it does because he spends a lot of time and effort on the details. That time and effort is non-negotiable. Without it your images simply look... well.. CG. Reality is quite messy and random. Generating messy and random on purpose is quite the task. I can count the number of images on my fingers which passed my test, which is, the complete lack of tell-tale CG signposts. Those images are produced by people who have sunk THOUSANDS of hours into the craft. There is no easy path in CG... it's just plain nasty, but sooo worth it when you finally start producing images that fool people. 'is that a photograph?' the sweetest thing I have ever heard.
good luck!
Ian