Maybe, maybe not. I tend to think that wherever life can arise and evolve, it will. I also tend to think that, all the challenges to life notwithstanding, it's unlikely that the origin and evolution of life is so hard as to make us the only example. (In that case, one might ask how we got so overwhelmingly lucky. Zero planets with life would seem far, far more likely than just one. Maybe an explanation would be required as to why the universe is so finely balanced with respect to the origin and long-term survival of life?) Anyway, we haven't even settled the question of whether life might exist on certain other bodies in our own solar system, many of which are outside the "habitable zone."
As for why the galaxy isn't crawling with spacefaring beings, there could be a number of reasons. I know we're talking a cosmic blink of the eye, but a lot of people of my generation, who sat glued to the TV as Neil Armstrong set foot on the moon can't fathom why we haven't colonized the whole solar system by now. We haven't even been back to the moon. It's not technology that's stopped us. It's sociopolitical factors. Although, sending robots into space is one thing and living beings quite another. I'm not sure we've figured out even a fraction of the challenges needed to make permanent colonization of either the moon or Mars possible.
I find the idea of multi-generational spaceships fascinating, but they aren't toys. They pose a lot of challenges, and not just technical ones. They also pose psychological and social challenges, and in the end it could be that they just don't work out very well for anyone. How can we possibly know at this stage of the game?
As for robotic probes, sure, we could send a swarm of them out into the universe, but how many politicians are interested in funding something that won't return results for hundreds, thousands, or millions of years? Maybe that just doesn't happen very often. Maybe in spite of our insatiable curiosity and our wanderlust, our home planet is the best place for us, after all.
We can speculate to the stars and back, but there is just so much that we don't know--so much that we don't even know that we don't know--to be able to have any confidence in any answer to the question: are we alone in the universe? But I fall back on this: in such a vast universe, even though life may be hard to make and maintain, how likely is it that it happened once and only once? Probably not very. So since we know it did happen once, there's a good shot that it happened at least a few other times, too.
