extremely good. the details with stuffs laying around and on the wall looks like it it is real

I'm pretty sure some parts of it (such as the stuff on the floor) use real life reference photographs. They often do this with detailed anime backgrounds as well.

There might even be some CGI. I find it hard to tell with how low the resolution is, but the right chair and the 'frame' (?) of the window seem kind of CGI to me.