Two counter points:
1. I thought that the amount of particles was far greater than anything I have seen on either current gen console and frankly was overwhelmed. However, as both of us have witness, the collision issues affect some of them. As you aptly put, these are early days yet and I suspect they didn't program those "inaccessible" portions with collision detection. But given its presence, it requires repairing.
2. While I absolutely agree on the recoil part, given the nature of the gun, it may not fit. However, more traditional weapons that fire solid projectiles accelerated by rapidly expanding gun powder should replicate KZ2's spread and ballistic profiles.
Finally, I think was the one of the first people to notice that long time back. You've got a good eye.