The game looks faithful to the GBA versions (which definitely isn't bad), but maybe a little too faithful - it looks EXACTLY like the GBA games, but in 3D - it really doesn't look like they added anything, other than fancy graphics and cinematics. I expected more.
Here's a few things they added:
-Status Menu contains things in the SNES games that were cut out of the GBA games, for instance fire/lightning/wind magic is split up separately now (it was combined as one in the GBA games)
-Skills are back! They specifically state on the japanese page that the skills from Seisen no Kiefu and Thracia 776 return.
-The new push attack lets you push an enemy or ally one space away. Whether you can do it depends on your weight stat. I guess this is for strategy, but it remains to be seen how useful it is.
-New classes, like beastman, birdman, and dragon. Pretty much they morph into their respective animal.
-Height seems to be a factor now. Archers may do more damage from a taller height. I'm not 100% sure about this though.
Overall i'm pretty happy with it, and i'm sure there's more to it than that. Having a new cast of characters and plot also helps as well, one of the things Fire Emblem is known for is its varied cast of characters. Each game seems to have their own devoted following because of the characters.