This is a half-formed setting idea. What I wrote here is something of an introduction; it's pretty much all I have on it & all I'm likely ever going to do. It's free to a good home. Whoever wants it can run with it.
It would work best as a one-shot or mini-campaign, as the 'stranger in a strange land' angle doesn't hold up well for years of campaigning. I envisioned the aliens as being a little smarter (or just further along in their cultural development), but less mean & aggressive than humans. Otherwise they are remarkably like us. I didn't put any consideration into appearance, cultural specifics, or even a name. They are background elements that provide an excuse to accelerate people from earth's recent past to its near future. How would the sensibilities of someone from the turn of the last century impact the world of tomorrow? What exactly does this future hold? I'm leaving these questions up to whomever has the answers.
You are the best & brightest that the your century has to offer.
In 1905, a radio receiving station picked up irrefutable proof of the existence of an extraterrestrial civilisation. Within the next few years, communication between various governments on both worlds devolved into an electromagnetic shouting match. In 1911, Great Britain and her allies created an aerial platform into the upper limits of the atmosphere. From there, a series of great cannons & rockets launched a squadron of brave young volunteers at incredible velocities to face the inhuman threat. These heroic stellar soldiers knew that it was a one-way trip. For their countries and their planet, they went anyway.
Both sides abruptly ended communications while faced with greater problems closer to home. Months later, the travellers reached their destination. In the interim, many years had passed on the alien world. The extraterrestrials were engaged in a devastating war that ravaged their world, just as--unknown to the newcomers--their own planet was in the grip of the Great War. The alien world was torn apart by the long conflict. They had been worn down by the fighting, and their resources were dwindling, as were the numbers of young soldiers involved. Though more advanced in the sciences, they were weaker in spirit than the human newcomers. The bravery and fighting strength of the earthers easily overcame all resistance. The three weary sides in the alien conflict could not withstand a fourth front, and sued for peace.
Part of the terms of surrender was handing over to the humans the alien's superior knowledge of the sciences. They constructed a light-sail for the surviving human's long voyage home. All of the alien nations contributed to the project, the first time in their history when all cooperated. With pride in their hearts and victory on that most foreign of shores behind them, the stellar soldiers returned home, victorious.
By the time they had arrived, much had changed back on the home front. Nearly 150 years had passed since they left. The Great War came and went, and another followed, all while the brave soldiers were on another world. These far-reaching servicemen had been forgotten by all but the most astute historians. They had been assumed killed during the mission long ago. It is a strange new world that they return to, where the advancement of the human species had brought greater learning--but no greater wisdom--than the advanced technology & scientific knowledge that the soldiers had brought back.
It is now 2058. You are even more of a stranger in your own home than on the alien planet.