Never ventured into this forum before, but as a working scientist, I figured I should pop my head in.
Background: Genetics. I currently do research related to mouse and human genetics for a biotech/biopharmaceutical company. Developing genetically-modified mouse models of disease, learning more about possible drug targets, doing genetic screens - that sort of thing. I got my PhD in Developmental Genetics from Cornell.
As for why I love science - I've loved science ever since I was a kid immersed in sci fi books and TV. I love science because it is ever greater knowledge of how the world works that enables us to move human civilization forward into hopefully a better future. I love biology because what could be more interesting than the question of how we ourselves, and other life on earth, work? There's no more marvelously complex system in the universe, that we know of. Each of us is the product of billions of years of evolution and selection, and it is remarkable what that process has produced. I love genetics because to me it feels like the most fundamental level of biology - maybe the operating system on top of which everything else functions. I feel like the things we are able to know and do, and will soon be able to do, in human genetics will constitute a major revolution and not just in medicine, but in all aspects of human society. Biotechnology in the next half-century will have as big an impact (or bigger) on society as computer and information technology had in the last half-century. Lastly, I like working in industry because I like seeing the direct connection between knowledge generated in research labs, directly translating into the development of new medicines that really help people live better lives, and in some cases even save lives. It's gratifying work.