Keep in mind that we are a very social species. We've spent nearly everyday of our lives in daily contact with other people. Attempting to put yourself in an imaginary situation where you could bear witness to such a person is a pretty difficult task to achieve. Even in cases of children being raised in some kind of isolation there has been minimal human contact (someone had to feed Anna still), or animal contact (i.e. feral children). Besides the obvious technical difficulties pointed out here, we can assume the child would be nearly mentally retarded. It seems impossible that the child would learn to feed itself. Without developing speech the child's analytic skills would be broken down into some primal instinct-driven chain of basic stimulus-response functions. This will essentially eliminate the possibility of our conception of "personality" to develop.
When you break it down into it's most basic level you see that personality is a collective system of responses to socio-environmental stimuli (or cues). You laugh because you find a joke funny. For other people that joke (stimuli) provides no response (laugh). There is nothing objectively inherent to a joke that makes it funny. It's a response to acquired dispositions to certain acts of behavior (laugh, get embarrassed, scold the joke-teller for utilizing dirty humor, etc.). For our fictional human a joke isn't even a stimulus. It's noise with no meaning.
There would be no personality. There would be no innate knowledge of personal grooming, exercise, love, etc. All of these things require some background - something to base its response on.
Perhaps the child could learn to feed itself, pleasure itself with genital stimulation, build very primitive shelter, and maybe use basic tools that require minimal shaping. There would be a number of instincts that could take over, but I wouldn't say with certainty what they would could be. Keep in mind, we have evolved as a social species and any instinct we may have will probably have some social conotations.
Either way I highly doubt anything impressing will develop. Definitely take into consideration the fact that any thought on this matter is completely theoretical. There have been no cases studies of people being raised in complete isolation.
Besides the clear limitations and ethical aspects of such a scenario it is a cool question and would provide and interesting thought experiment.
