I have to agree with Basse on this one, on all-points actually.
My guess is that most are too polite to give any “strict” critique
so I’ll add to Basse’s comment’s to help you out.
The characters need life as Basse implies, you could add to this
by manually editing the face meshes. This is of course quite
complicated, but then again…this is a complex image and it
needs your attention. Try watching some fun-family photos
in your family album…look at your sisters & broters or
mates & girlfriend and whatever people you have around and
see for yourself their facial expressions…try to take some
pictures…and study it. Look at some movies…freeze frame
and check out the facials. Learn and study…and Apply!
The anatomy of some of those characters seems a bit
twisted and mis-shaped in various places (eg. the boy
laying on the table working on that computer…try to
fix the defective anatomy…it’ll help the character look
less like a deformed-3d-doll 
Mr. Linus looks good though, some deformations on his
clothes (especially the upper arm section) doesn’t look
convincing.
And for the light…and textures…they go hand in hand
so the first thing I personally noticed was the bright-white
computer…
Believe…if you placed a computer monitor like that out in
the African plains…you’d mess up the bright-white in less
than 10 minutes. It’ll be dirty, scratchy and the reflections
of the sun/weather and enviroment MUST match colorwise.
You don’t have to use slow raytracing & radiosity to do this
you can do this by planning your textures properly. Color
the textures FOR the enviroment you’re planning to use
them in 
More contrast would seriously help this somewhat plain
and dull image. It’s not a dull image per say…but the
light actually MAKES the image dull. You’ve worked hard
on this image - give it the final extras it deserves!
Now that you’d have to swallow all that harsh critique
I’ll add the friendliness last 
I do like:
- The concrete table/bay. Excellent concrete and shading
Very beliveable.
- The African pottery! Nice detailing on the big pot.
- The grass looks dirty and thick! NICE! This is actually how it
looks in real life there. I hope this doesn’t change when you
change the lighting…if so…try to keep the quality of
the ground and grass - it looks REALLY nice.
Good luck and work on it!
/JoOngle