That's a decent size for a web browser, software which, after all, doesn't do all that much. Because Opera is small, it's fast. It loads quickly and displays your chosen page before you expect it to. Also, because it's small, you can run it on older PCs that strain under the weight of the popular browsers. Opera has also mapped its entire command set to the keyboard, obviating the need for the mouse, making it the browser of choice for the visually impaired and RSI sufferers.
Opera has some drawbacks, of course.
It can't handle Java code. These problems, they say, will disappear in the next major version, v4.0. Opera's main advantage to me, however, is that Opera Software has no incentive to please anyone but its customers. You won't find Opera proprietary file formats or Opera extensions. If any one set of proprietary software takes over the Web, we'll all be at the mercy of the owner of that software.