IMHO, here is how I would have done Mass Effect Andromeda.

So the Andromeda initiative sends multiple ships to another galaxy. It turns out that one of the people they sent got a big lust for power and turned the initiative into shit, creating a rogue faction among the crew, sabotaging life-pods and provoking a war against some alien races, so the real ennemy would be a human threatening the whole initiative. It turns out that rogue agent was indoctrinated by the rippers, he smuggled modified ripper tech on board to allow the creation of a neo ripper like race which would have colonized another galaxy and restart the whole cycle again. Your mission would now be to re-unit the Andromeda initiative, make peace with aliens that were wronged and stop the potential re-appearance of a neo ripper race.

So some people might argue "Well, rippers only exist in the Milky Way". But how can a race that can survive in dark space, for hundreds of millions of year can be stuck to a single galaxy? I took sentient races 600 years to reach Andromeda, the reaper had plenty of time to do the trip, furthermore, didn't they build the mass relays?