Not having a running game is killing Brees. The Saints won last year because they had the 3rd best rushing attack in the league. It gave Brees a little breathing room. Now there is no run game, and defenses just have to defend the pass. The receivers should be stepping up and they aren't.
Everything is just a little bit off. The O-line doesn't pass protect for that extra half second or second that allows Brees to hit something more downfield. The receivers don't quite get open enough to allow Brees to trust the pass. Brees can't quite pull the trigger downfield as he had been doing. The run blocking isn't quite good enough. The play calling just isn't quite inventive enough to keep teams guessing. It's a multitude of little things adding up to one big thing. A stagnant and inconsistent offense that can't get it done in the redzone.
You're right and it's surprising too. I thought they'd come in with a champion's swagger and pick right back up where they left off last year. Granted, injuries have slowed us down the last few weeks, but I said it before, I'd rather be healthy towards the end of the year. It's way to early to call the season a disappointment.