That looks very good!

I don't often see green surface layers go well with objects, but here it works really fine.
The only little crit I have is that the grasses are a bit noisy and I see that you've rendered this at AA4.
Perhaps you might re-render this with AA6 or even 8, it will really make a difference.
Detail 0.75-0.8 and AA6 will probably be best speed/quality ratio.
Cheers,
Martin