I think adding aliens into a futuristic world like fallout has always done well, be it in movies, books, comics.
They are done well. Provided that the
story revolves around them. H.G. Wells'
War of the Worlds wasn't about mankind destroying itself and then aliens coming out of nowhere. It was about Martians attacking Earth, and then humanity trying to defeat a much stronger enemy. One that couldn't be stopped by bullets, missiles, or anything we tossed at it, but were finally defeated by nature's strongest weapon; microbials.
Fallout is a futuristic, 50s utopia turned into a post-apocalyptic dystopia, and then mankind trying to survive and rebuild itself after we were kicked back to the stone (and plasma rifle) ages. While we still have some advanced technology, most of mankind doesn't know how to utilize it, and for those that do, they think only for themselves rather than for humanity as a whole.
Now then, like Boradam said, it'd really only be good if it were a Wild Wasteland experience, as some of us, like myself and Styles do not want to see anymore aliens, but other users, such as yourself, would like to see aliens.