I think the demo went a long way to assuage a lot of the fears surrounding the multi-player. Of course the marketing people are focusing on the multiplayer aspect since it's a major new feature and one I imagine they're hoping will draw in *new* customers who may not normally play single player games, let alone RPGs.
As for how they're reporting on the game, I for one am glad that spoilers have been largely kept out of the trailers and I'm confident enough in Bioware's track record that I'm not concerned about the single player either. Maybe it's just me, but I *want* to be suprised!
To answer your questions though: yes, Sheen is definitely back as TIM. Yvonne Strakovski I'm less sure about, but Miranda, like all former (surviving) squadmates, is also definitely back.
[Edit] For those still looking, Play.com has the CE back in stock for all platforms, complete with the N7 wargear pack. No telling how long it'll stay that way of course!