@Sicarium: You could always just kill them all...that works too.
It was explained that the keepers were supposed to do a thing to turn the Citadel relay on (The best invasion point, it's like if Russia went to war with the US and their entire army teleport to Washington DC in seconds) plus given how the Turian councillor treated the story, it wasn't much of a heads up, if Sovereign hadn't been so much of a video game villain and brought Saran back from the dead then the Reapers would've won, that's it, simple.
Agreed, they made a huge series with a massive story and it just sort of ended, no boss fight like ME1/2 (Unless you count Marauder Shields, he shall be missed) it ended on a very Lost style ending, that a lot of people theorise just happened in Shepards head.
In the grand scheme of things though, I think they've learned their mistakes, plus this won't be a "standard" Mass Effect game, they've said the main dude(Or dudette) won't start famous like Shepard did, they'll be a nobody then become a somebody.
Plus there's the feeling of exploration, it was kinda "there" in the other games but never expanded on, that's the reason for the Trek pun in the title.