4.5 months post- op! How's my hair density/thickness after my FUE transplant? (photos)

Based on your photos it appears as if things are progressing nicely.You are just starting the growth phase so sit tight.There will be a lot more growth in the next 7-8 months.

Greetings,Density is one of the most critical factors after hair transplantation.  Early on you may not be able to fully determine your density.  Density depends on various factors including the number of hairs  per cm squared, the thickness and vibrancy of hair, direction and design of hair.  Techniques for density vary from surgeon to surgeon.  In my office, we utilize a specialized technique that allows for optimizing density and found it to be helpful.  
Best,
Dr. Anil Shah

It can take 6 to 12 months after surgery to see results.  If you are concerned it is best to contact your doctor.  Your hair may actually look worse at the 4th month mark in some cases.

It is not often that we see more initial growth on one side than the other but the two will eventually even out, given time