First off, I want to address the size difference between the Gen3 and Gen4 grip since that is the main reason I bought the Gen4. The Gen4 grip is definitely smaller in circumference than the Gen3. The Gen4 is on the left. From the picture above, there doesn't look like much difference, but check the next two pictures. The first is the Gen3. The second is the Gen4. For a small hand, that's a significant difference. Staying with the grip for the moment, another big difference is the grip texture. I think I prefer the Gen3 texture. The Gen4 texture is a little more aggressive and might not be the best for carry or shooting hundreds of rounds in one day. I only fired 90 rounds after picking it up and noticed a slight redness and stinging in my palm. But that's just the opinion of someone with soft, girly hands. Report continued in next post because of picture limit.