Depressing and realistic? Or just pessimistic. Assuming aliens would want to come here in the first place, why would they? For materials? Why the heck would they travel light years for that just to grab some metals or gasses they can likely find in any star system.
I suppose it's possible they might just wipe us out, but in all the vastness of space there is really only one thing that could draw aliens here. They would come for same reason we want to visit other worlds - life. Life has to be the most precious thing in the universe. Even if life is abundant, and on ever planet in a mostly habitable zone around a star, the universe is so vast as to still make it scarce and amazing.
It seems most likely there would have to be something about us that they would want to exploit that would make the trip worth all the bother and expense. Maybe they want a client race to be slaves, we've already found that machines are damn hard to build that can do something as good as a human can do, except with very particular specializations. Possibly they have a need to be worshiped (Stargate). Instead, they may simply need to be in control of that most precious thing the universe can offer.
It could be there is something unique about life itself that they can devour or fuel their technology with(Vampire Earth, The Matrix). Perhaps the worst scenario maybe they are so xenophobic they simply can't abide anything that lives besides them(Berserkers). Most hopeful - they could want to better us...for a price (Uplift Saga).
Perhaps, as in Star Trek, beings would seek to make common cause with other beings for mutual protection and comfort in the face of more hostile aliens. However, as with the prime directive there are limits to the usefulness of non-spacefaring races. Plus, such races would be extremely vulnerable to exploitation and destruction by more advanced species. In the context of a larger arena of political games we might be wiped out, or enslaved just because another race might find us a convenient choke point or jump off point between them and their neighbors.
It's damn hard to predict what something with an alien biology and psychology would want or need, but it seems likely it would have to revolve around life.
In movies humans fight off alien occupation forces, explode alien ships, and mind-control aliens with the power of love. How on earth can we think that would happen?
