Earth is so wonderfully special because we have liquid water on our planet's surface. Not only that, but the amount of water is sufficiently small that the Earth's surface alternates between water and land.
This is particularly beneficial for life. Land-living species on Earth only exist where water is available. I'm too lazy to google today, but I have read that there is a desert in South America that is the world's driest place, and that is the only place on Earth where scientists have failed to find live.
Similarly, shallow water near land is ideal for many aquatic life forms. Life exists throughout the oceans, but nowhere is aquatic life more prevalent and richer in species than in shallow water near land.
Therefore, if there had been more water on Earth, and Earth had been a water world with no land, conditions would have been slightly less favorable for life. That is most certainly not to say that life couldn't have existed on such a world, of course.
But could we
Could we have built a technological civilization? Remember that under water you can't make fire. Could we have built great buildings and great machinery without fire?
And how would we have communicated? Would it have been possible to create languages nearly as intricate and rich as our spoken languages, if we couldn't speak the way we do now?
And how would we have stored knowledge? We couldn't have had libraries, books, computers. I don't know about you, but I'm not too optimistic about the possibilities of an entirely aquatic, highly communicative, great technological aquatic civilization. Remember, Atlantis died when it sank! (So it may never have existed... that's beside the point here.)
Would we have been mute mermaids, swimming in our water world in silence?
This is our world. This is us. We live here because our world has just the right amount of readily available liquid water.