I happen to be starting another playthrough of ME1 right now (FemShep Sentinel, should be fun!) and I really think the opening is perfect as-is. Brief text scrawl, flying out through the solar system towards the Charon relay as Joker narrates and we follow Shepard from behind to the bridge, the jump, banter with Nihlus/Joker/Alenko, quick conversations with Presley, Jenkins and Chakwas, and then the briefing then drop onto Eden Prime.
First-time players of the game didn't know anything about the universe either or what the titular Mass Effect was, and that wasn't a problem in terms of the gradual intro.
I think Ashley Alenko's death and Saren's escape would be a suitably low ebb if you play up Shep's relationship with her from the beginning, right from the opening bridge scene as a best friend and longtime companion even.