Cutting the metal siding was the smart thing to do so you can get your ledger board properly attached to the building. Was it attached properly? One of the biggest reasons for a deck failing is the ledger board. I like that he used joist hangers. I've seen a lot of decks built on this site that didn't do this.
Your picture shows the wrong side of the deck to be addressing. What was done on top of the deck? The metal siding looks like it will unscrew so that you can get flashing under it and on "TOP" of the deck. Follow the path of water and stop it from getting onto the ledger board.
I see something silvery in the gap between the bottom of the ledger board and the siding. What is that?
When I look at a deck, the first thing that I look for is diagonal bracing when it's more then a few feet off of the ground. This cuts down dramatically on how much movement you have on the deck. Armatures forget this all the time. Next thing that I want to see are beams that the joists are resting on top of. Another big armature failure is not using beams and framing up all the joists to support the load. Then attaching them with nails. Nails and screws are never to be used for supporting a load, they are just used to attach lumber and hold it in place, not support a load. I can go on and on.
Again, what does the top of the decking look like next to the building?
