Aluminum back panel can be subject to scratches and dents, so much so that some shipped scratched from the factory.
Case is so light that it almost feels fake and some users may prefer the "heft" of the earlier iPhone 4S or iPhone 4 models.
Camera lacks optical zoom.
Battery life can be shorter than official estimates, particularly for mobile data use.
Lightning connector is not backwards compatible with the earlier Dock Connector or thousands of existing third-party accessories.
Nano SIM card may be a hassle when traveling (although a larger SIM can be cut down to fit).
Unlocked and contract-free models are considerably more expensive than contract encumbered models and the iPod touch line.
Ultimately, if you need a smartphone, the iPhone 5 certainly is a solid choice.
Site sponsor PowerMax has a good selection of used iPhones -- including iPhone 5 models -- available for sale free of sales tax.