Personally, I don't find anything listed as a "disappointment" at all. With an "s" series release, most of us are aware of really what to expect (upgrades internally, but not an overhaul of the hardware, screen size, etc), but I guess the same doesn't go for the general public. Either way, I found it interesting to read the opinions in the comments section.
Five disappointing things about the iPhone 5S | iPhone Atlas - CNET Reviews
Five disappointing things about the iPhone 5S | iPhone Atlas - CNET Reviews