The cultural/chronological clash doesn't have enough balance and there's to much evenness in the gaps. The more basic patterns/prints/paintings have to much white space with no detail to capture them with. The bottom paintings are also a bit to low to be natural and stretch out the feel of the wall uncomfortably so, and there is space above the hallway that is abruptly cut off.
The floor also doesn't have anything to spread out the color, like a rug, and instead relies to much on some cheetahs that abruptly start near what seems to be romance and renaissance era works. There is also no strict cut off for the borders so it all blends together as a single mass instead of a section. Instead of having the vent be surrounded and be stark white, you could also paint on it (with the appropriate paints) like with the power outlet.
There you go! It's not all that good, but it does have a little better vibe. I'm still a bit inebriated from last night so I hope it doesn't look to off putting. For the empty space below it'd be best to have floor items there, like the cheetahs, but I didn't know hot to move them over since I don't have photoshop.
When it comes to portraits it's best to have them around eye height or a little higher. Also don't have to many darks close together, and vice versa with starks and themes.
Though don't take my word for granted, the only interior design experience I have is 800+ hours on TS4 so I'm not a professional at all.
You actually made a large gallery wall work and not feel cluttered, I’m impressed
