There is much in common between Science and Buddhism simply because both are based on logic. Science doesn't ask us to a assume anything based on faith and similarly the Buddha taught that we should check his teachings against our personal observations and experiences, not blind faith. Just as in science, Buddhism requires the practitioner to be pro-active and to be personally involved in the results he or she would like to see via the practice of Buddhism. This is very much unlike some religions where we propitiate a supreme being and then hope for results.
More and more, reincarnation has been proven scientifically and a quick search on You Tube will uncover endless accounts and documentaries of reincarnation from people who are not even Buddhist. If reincarnation is a fact, it must also follow that karma is a fact because karma and reincarnation go hand in hand. If karma is a fact then virtually everything the Buddha taught is correct.
As for the things Science and Buddhism say makes us happy, one need not convert into Buddhism to be happy. In fact a lot of the spirituality in Buddhism is pure and simple commonsense which are not so common because people's minds are often clouded by wrong views and perceptions. If we truly understood what makes us unhappy, who in their right mind would not want to apply that? At the core, Buddhism teaches us to be happy and to make other happy.