Nine times out of ten, when a new client doesn't like the job you've delivered, it's because the images don't match what they've visualized in their mind. This is exacerbated by their assumption that what they are seeing in the proofs will be the final look of the project.
When you encounter this, and you will if you shoot enough, try to ignore charged statements such as, "I thought I had communicated what I wanted, but clearly I did not." and get to the root of the issue as quickly as possible. Often, you'll have to do a little detective work to find out the adjustments that are needed.
Once you've figured out the direction you need to pursue, respond with an even voice addressing their concerns and assuring them that the project will still turn out well. I often have them choose their favorite image from the gallery, then apply the changes to it for review. Typically, the feedback will be more positive on the second round, allowing you to build some momentum. Once you get one image to their liking, you can apply those changes to the other selects.
You'll probably spend more time on this project than you had originally planned. But it's important to make the client happy, if possible, because it will lead to repeat business and referrals. Think of the extra time you're spending as part of your marketing.
Clients don't always realize that an image has to start somewhere, and that we have the talent and tools to take it in many different directions. Stay confident and listen closely. With a little luck, your cranky client will soon be a happy one.