What is it that makes this scene still feel CG? (In other words, when people look at this and say "that's not real" what are the things that give it away)
Update: I've incorporated some of the feedback so far and changed a few other things too. So here's version two (below the version 1 image)- with a little bit more stuff in the room and some changes on lighting. I next need to add grunge maps and the like.
Again thanks to everyone for the feedback given so far. If anybody has any comments on version 2 they would be greatly appreciated.
Thanks Everyone! Awesome comments. I'm working on incorporating them!
I don't know that you need to tweak the model itself much, but maybe a little work on the textures, and maybe some clutter.
One easy thing to try is taking a photo of a real wall and doing photo projection onto your model wall. See what looks different, and see if you can replicate it. If the photo gets you what you want just having it may be enough to get you there. Or, maybe get you there with a bump map generated from the very same photo.
My 2c below. There's a lot there, but photo realism is tricky.
It doesn't feel lived in. Like Adrian said, dust might help. So would a little wear and tear on things. Some dings in the paint on the walls. Crinkles and/or curl to the poster. (Along with tacks, or spots that look "pushed in" if you're using that double sided putty stuff). A little dust or grime on the windows and blinds. Maybe a bent blind or two. Dings on the chair, music case, and music stand. Texture to the wall paint and baseboard paint. "Multiple layers" of paint. Unless it's a new apartment, especially the baseboard should look like it has many layers of paint on it. The backpack looks really "perfect". It's pretty square, the texture's a little more cloth than typical nylon, and there are no bulges or sag at the top of the pack if it wasn't full. It's industrial carpet, but it looks a little flat. Feet and/or rubber grommets on things.
The blanked feels a little thin, more like a sheet, and there are no wrinkles in it. Even if the bed was made "perfectly", there'd be a dent where the backpack is.
Like Omar said, lighting. It can be a little bright because it's daytime and bright walls, but pick a lamp, or recessed spot in the ceiling for a "regular" light. A few dust specs in the air.
The desk and chair seem a little out of place. More like church auditorium pieces. I guess if this is an apartment instead of a dorm it might be affordable furniture. . . but it just seems off. If it's a dorm, it'd be built in furniture, almost perfectly fitted to the room. . . for U.S. colleges at least. If it's a student's room I'd expect more Ikea like furniture, or heavy but worn used furniture.
There's a lot of space in the room, which might work for a house, but in front of the desk is a lot of unused bare floor. No clutter of clothes, papers, nick nacks. Maybe the person's perfectly neat. . . but it's a lot of bare space.
Edit: Lots of small edits. See Ian Hubert's lazy tutorials for tips on crinkled paper, and maybe some noise on the windows so they're not perfect.
Edits all over the place. If you go with a generated noise map for paint, look at the CGCookie scattershot plugin so it doesn't repeat too regularly.
This is really good modeling!
Currently, its too clean
Adding dust and dirt will go along way towards realism, not just on surfaces, but also in the atmosphere
also the bed sheet is too perfectly placed, add some wrinkles and creases to the surface, especially where the bag is placed.
Having a stand with sheet music suggests an instrument should also be in the scene, it feels unfinished, missing details, thus more CG.
That's a tough questions. There's always that je ne sais quoi when you're looking at a render that gives it away. The biggest one I'd say is global illumination and shading, how the materials are behaving when the light hits them. Shadows are a big one, we tend to want to illuminate every corner and not let light bounce naturally. I have always thought that color grading also plays a huge part.
Want to do an experiment? Take all the color out of your image, turn it to black and white and see how it instantly feels more realistic. There's something about colors that you need to hit for the image to feel more grounded in reality. Too much color and saturation gets you into cartoon territory without you realizing it. But to hit that sweet spot of realistic saturation is freaking hard, because it's so subtle.
In your image there is little to no bump, surfaces have no porosity or imperfections and that gives it a CGI look, those perfectly flat surfaces are characteristic of computer generated images. Also the little details matter, we tend to do the broad things, have the bed, the chair and the table, but not the small things, like a remote controller and a pencil on the desk. Grunge is huge also, that dirt and stains on surfaces, scratches, all those details. So yeah, to get you render looking realistic is a lot of work, we tend to not go the extra mile and just say "meh it's good enough" way too early.