Been playing the EO1:U demo in Story (classic mode isn't available) and it's got a LOT of changes from the original.
New areas (at least one subarea), new classes/skills (Gunner has a pretty awesome low-level skill: Heals the front line every time she defends. 20HP heal with a 3SP investment when I only have 60GP? Ooo.), a more robust automap (sorry, I've already mapped this entire place once-- I don't mind being lazy), the grimoire stone system where you can use skills from other sources, rebuilt skill trees, and, my memory may be off slightly, but effectively bonus skill points. On an alchemist, for example, putting one point into the basic alchemy skill gives you one free point in each of fire/ice/lightning. Also, alchemists have entirely lost the toxin branch entirely.
There's a lot of QoL changes too, like vastly faster combat, movement in the dungeon, ability to teleport directly to the stairs if you've mapped that floor adequately, new buffs available in town (first one that gets unlocked allows for HP regen after every round), hidden passages being visible so you're not constantly strafing (like in EO4, how they're usually flowers visible), etc.
The layout of the second floor is entirely different too-- the Ragelope is still introduced, but it's bigger and has a new FoE with an unprecedented movement pattern (not that it's complex, but it IS new, as far as I can recall).
Unfortunately, Lolimedic is unavailable in Story Mode. However, Caduceus is still there, so the frontline medic is still sheer awesome. ^_^