If you're actually looking for an answer, as opposed to just wanting to express your beliefs, the reason is that our greater capacity for consciousness and reason, as mentioned by nebbykoo above, gives us the potential for moral perfectibility that is more-or-less absent in other creatures. As such, who we are and what we may become is under our control, in our own hands, and, as such, the greatness that we can achieve is higher than that of any animal. Whether we embrace our potential for growth is, in each individual case, uncertain, but the lone fact that we possess this control makes our destinies more interesting than that of other creatures. We are the only ones who choose our fate. If, like a child, you want to ask why that matters, I will only be able to offer you that it inherently does. If there were a God, and we were to actually have some degree of free will, the uncertainty of how we would respond to that freedom would make us more interesting to observe than the creatures that do not.
