Late to the party, I know...
The only issue I see with it is that there is nothing between the shut-off valve and the tank itself. It appears to me that once you shut off the valve that the only way to remove the gas line from the heater is to remove the valve itself. This will leave you with an open gas line.
I would think you'd want a short piece of pipe out of the valve, then into a union, then into the heater. That union is what you'd disassemble in order to take the gas line off the heater.
On second look, I think you've got a valve at the other end of the flex line. If that's the case, you can shut off the gas there to detach the line from the heater and that makes the valve directly below the heater redundant and unnecessary.
Looking at the pics more closely, I just noticed that it appears that the mounting bracket holding up the heater is installed upside down. Take a look here:
That screw is through a keyhole slot. By design, the big hole should fit over the screw head so you can partially start the screw, slip the bracket over the screw, let gravity pull the bracket down so the narrow part is over the threads of the screw, then tighten down the screw.
The way this is installed, gravity will pull the bracket down so the big hole (the one the screw head will fit through) is over the screw. It is possible that, over time, gravity will work against this set up, pulling the heavy water heater down the wall until the screw heads are aligned with the big hole and the heater could come off the wall.
Now, it could be that this is installed in accordance with the manufacturer's instructions and all is good. Also, this has been installed for at least 2 years (as of the time of writing this answer, based on the date of the OP's post) and all is good. However, I felt obligated to point out this potential source of failure, since it could lead to spilled water (an inconvenience and pain and potential source of damage), and it could lead to a broken gas line that could cause an explosion leading to significant damage and possible loss of life, not only for this residence but for neighbors, too.
Should this be changed? I would. Whether you do or not is up to you, but at least you're aware of it.
If the screw head is too big to fit through the key hole slot, then this is a non-issue.