Familiarity. That's the problem. For as much shit as I give the contrivance of ME2's opening plot, the use of the Normandy being destroyed (and then resurrected) was a very effective tactic.
In ME3, it feels exactly like what a lot of people feared from the first trailer: no attachment to Earth as it exists in the ME universe at all.
The fact that it just drops you in with an awkward six month gap that has to be filled in with unwieldy exposition for anyone who didn't play Arrival doesn't help either.
Exactly. The player is completely detached from what is going on. There's no familiarity, no connection, and no association. Even characters like Vega are guilty of this, as the game
assumes an established relationship with him.
The game should have started with Shepard preparing for his/her trial. Anderson would suggest Shepard unwind a bit before the hearing, blow off some steam, and get some fresh air so he/she is ready for what is bound to be gruelling legal mud slinging.
At this point you're given a bit of freedom to wander around an Earth based mini-hub. You can speak to a few people, maybe meet some familiar faces from the past games, and get some solid footing as to what Earth looks like. Give the player the ability to control the pacing, a sense of empowerment. Hell, even play with them a bit. Allow them to check out where the Normandy is, grounded by the Alliance. Let them see it in front of them, but have a guard prevent Shepard from boarding. Show players something they own, and prevent them from accessing it.
Then, I don't know, have someone suggest Shepard go to the gun range as somebody wants to meet them. There you meet Ashley/Kaiden, and he/she introduces you to Vega. Use this as a means to tutorial some basic shooting/cover mechanics against targets, or even a friendly (and cheesy) non-lethal shoot out against one of the above two.
After doing all of this, and having the freedom to go about at your own pace, you make the choice to attend your trial. Just a couple of opening questions as well as the ability to respond however you'd like, and
boom, Reapers emerges from the clouds above. Bam, explosion, rarr rarr, and the rest of the tutorial follows much like the demo did, travelling across/through many of the locations you saw/explored just previously in the hub, watching the familiar sights torn to shreds by towering Reapers, as the people you were just speaking to are running in fear and being BZZ LASER BEAMED to death, as you make your way to the Normandy you can now board (or are picked up by Ash/Kaiden, whatever).
BioWare, hire me to make your introductions because I'm awesome and better.