I've never really played Fire Emblem.
But I have played Smash Bros. and holy crap Lucina is the worst. She's more of a Marth clone than Roy was (she shares one of his idle poses for god's sake) and isn't even visually distinct from him. It only matters if you can tell the difference from far away, but they look alike even up close, as Marth has become more and more androgynous with each Smash Bros...
The funniest thing is that Sakurai's reasoning for not putting Chrom in the game is "He'd just be another swordfighter like Marth and Ike." While I don't disagree that the roster can be oversaturated with a certain character archetype, and the one that is approaching that is swordfighters, this is just an absurd rationale to not include a non-clone when Lucina is as "like Marth" as possible.
Also, uh... The dialogue in the trailer had that anime-style stiffness to it, like I could practically hear the forced voices echoing off the unrehearsed scripts three inches in front of the actors' faces. Nowhere near as natural-sounding as the Kid Icarus characters. Kind of an extreme nitpick. But I mean, Sakurai helmed Uprising and its English voice cast was good. Really good. So, I mean, I guess I can't complain as long as the new voices hired for characters who haven't had them in their own games recently are good. And Ness can pronounce the word "Flash" this time