That image is a bit of a mixed bag..
Let's see the things I've noticed.
1. The diagonal line of the desk to the left doesn't match the wall, and neither does the window frame.
Can't say I'm an expert on perspective but it looks strange to me..
2. a) Some things are anti-aliased and some are not, personally I'd go without AA.
2. b) If you have to use anti-aliasing, don't overdo it, currently it's quite blurred.
3. The post-it notes looks strange when their sizes differ like that.
4. You use a lot of noise for textures, again a personal thing, but I'd prefer to see patterns instead, or just a single clean color.
5. Try making more use of highlighted edges instead of just outlines, sorta like on top of the chair.
It gives everythinga more fresh look.
6. Don't be afraid of making things larger, especial the wooden strips between the wall and the floor, the door, frames on the corkboard, etc.
(actually the door frame seems to be missing)
7. The text on the notes, etc, looks quite odd. Try using a lighter color, and some AA in between could help.
It's quite a list but I hope it's helpful
edit: A second look at your image (and an attempt at an edit) tells me you're using way too many colors and anti-aliasing on basically everything which makes it look too undefined. It must also be really hard to work with and take hours to add all that AA.
Try reducing the amount of colors, less is more. Also a bit more contrast between colors would also be good make it look extra clear and crisp.
You want some things to popup out at you, right now everything feels too subtle.
Some things you should keep in mind, use less colors and try to add depth where you can, like edges popping out, the door for example can be pushed a bit deeper into the wall, the strips of wood down on the walls can be made to look thicker, the edge of the desk can protrude a bit above the drawers and the window can also be pushed a bit deeper into the wall.
You have a huge room but you're being a bit too minimalistic.
