I think it needs more weight in the center. I would start with the larger ones and work out, up and down with the smaller sizes.

I'm sure it's just me (I tend to have a hard time letting go and being too free) but when using a lot of mismatched items, I think it looks best to at least have one thing in common on all of them. Color is usually the easiest.

You've got every shape plus a mix of modern and vintage and traditional plus a mix of woods/metals. I just think, for me, they'd play nicer together if they had a common color or at least a common color family.

I'd also start big in the middle and go out.

I think there's too much space in the middle. I agree with the others about starting big from the middle and working out.

I found out when doing our gallery wall that I like symmetry and can't pull off the free flow/add later arrangements. I tried a gazillion arrangements until I found one that worked. Just keep trying different things. I found taking photos really helped me to 'see' them.

I agree about matching the frames would also look more cohesive.

I don't think you need to have the all frames match or be in the same color family. My frames are mix of styles, shapes, color and materials? I think it adds more interest. Some of your frames seem to be a bit too close together. Do you have room to spread the frames out a little bit. I agree that you might want try something larger in the middle, perhaps a frame that holds multiple photos. It would give you some weight without having to have large photos.
On my photo wall I have 8 multi-picture/collage frames. Initially, I layed out my frames on my great room floor, played around with them and then recreated the arrangement on the wall but over time I have just done random free flow add on to the gallery. I like the casual, not perfect look.
Here is my rendition: