I'm not aware of a fan site that reveals the new units, abilities, spells, etc. introduced in WoTN: Fire and Ice. If you know about one, let me know.
Otherwise, with an obvious
spoiler warning, what have you guys seen that's new?
I've only had a little time with the new campaign, but I've noticed that polar bears have a new icy claw attack that damages and slows, and I've been trying out a new level 4 viking unit called a Mystic which can go into trances to buff your defense or control an enemy. Some undead I fought have a new trait, too, called Necro energy, which builds up as the battle goes on and let's them regenerate destroyed units. I didn't let any of them live that long to see it happen, though.
Edit: I forgot to mention combat experience for units. Your units get a little XP each time they act, and they get a small, stacking benefit on ranking up. For example +2 attack and +1 defense at rank 2 (rank 1 means no xp and no bonus). The bonuses don't seem to be customized in a way that I can tell yet. I only have vikings right now, but they are different levels and types, and they all got the same thing at rank 2. The one army I have at rank 3 got another +1 attack and +1 critical chance.