Dont be affended that pretty typical…I for example did take a look at your render but just didnt have the time to critique:( After looking at it closer I have a few quick comments.
First of all it a good start…I like the concept…first to clarify this is Blender internal renderer not cycles?
I have had the same issues with grass and All I can tell you is just keep working it. I would suggest reducing the number if children and increasing the parent particles and then reducing the amount displayed to like 20% then when you work in model space its not so heavy but will render all the particles. The reason for this is that children dispers around the parent and you have less control.
Now your textures need some work…try to find good reference images…like the basket ball its a bit too shinny and the papers should be less perfectly flat
The wood blocks and train should also be textured at least with a normal/bump map indicating wood grain.
Is the bike modeled or a flat plane with a transparent PNG image? If its modeled great job if not its a good illusion:)
The stones on the sides are ok but I think your more likely to see concrete curb which is a smoother transition from the asphalt not so square. Check some reference images. You could stick with the stones if you want but the material has too much spec and needs more normal bump texture.
The pavement is probably the best texture…you did good there.
My biggest issue is the road just ending kinda abruptly as well as the grass. A trick I have learned is to put a little curve (downward)on the end of the surface so the grass and pavement would follow and better hide the transition to sky, almost like a bit of a hill.
Finally ad some serious glow from the sky like he is walking into heaven. The glow should overlap the pavement and grass to also better blend the ground to sky. And a little DOF would do wonders for this scene…it also helps blend and hide imperfections such as the old man:)
Hope this helps sorry if it long
Good Luck and Happy Blending:)