I agree, that's a pretty nice image. The only notable issues I see are the low texture quality of the foreground tree (that's a known problem with that model; you could try adding some procedural texture over the top, inside the object Parts Shader...), and the banding in the sky which is probably just due to JPG compression. You could also use some more variation in size and color for the grass - use the new color tint options in the population (v4) for example, and ideally you could use some more varieties of models. But in terms of the scene in general, it's quite nice.
- Oshyan