"Imbuement has been removed from the game. I loved the flavor of it, but players didnt realize they could be casting spells with their champions. And it makes the champions less unique if the thing that distinguishes them most (their access to spells) is missed. It was a bit of complexity that could be dropped without losing any good gameplay. Most notably since all the champions can cast from the start when you find enemy champions in the wilds they start lobbing spells at you. For those of us that are accustomed to attacking lone champions in the wild, seeing them starting combat by throwing fireballs at us is a bit of a shock."
I suppose that Champions without ranks in any Element, cannot cast spells except by Annointed by Fire and such. I'll miss Imbuement (remmant of an old age) but it certainly didn't make so much sense to be able to increase the Elemental ranks of the non casters.
"For example, I like the ability to recruit monsters. But it’s too hard to get and not rewarding enough when you do. So the Bonding Ceremony and Mercenaries techs are gone. Instead the ability to create those improvements comes on other techs that were already worth getting (higher level improvements that allow you to recruit things like dragons and ogres are still special techs). Most importantly when you train a monster like a Drake or Troll in your cities they will start at the normal level for that monster type, not level 1. So your drake will start as a level 6 drake and capable of doing some damage."
Must take note to save that removed stuff before the patch. I have never recruited monsters beyond the "Lets check them" factor so it'll be nice to have some real reasons to recruit them. 
"The magic tree had some exciting things hidden in it but it needed some work to bring it out. So we created a few new craftable items like magical staves, enchanted robes, etc. Along with this came 30 new unit’s designs, 3 for each faction. These include trainable Mages (units with magical staves that shoot fire or ice), mid-level warriors with magical weapons and end game units that have the best enchanted weapons, armor, traits and mounts the game has to offer. If you see these marching over from the AI player you may be in trouble."
Ok, this comes from the modding side but I need to ask: shouldn't be possible to have optional branches in research? Like a whole branch that only appears if the first tech of it (which has less than 100 of appearing) does appear? Because right now I only get crashes. I mention it because I like how some techs are not available in all the games but they are single techs at the end of a branch. I suppose that for balance, that's better? Also, I know that the tech tree are quite simple in nature but... would be a zoom option a bad idea?
On topic, I loved the artifact creation in MoM and although I do not expect to get something like that for FE (at least not base game?), I welcome more magic items than a few rings, weapons and armours. I don't think that those things should be easy to create but with enough research and a good city structure, the channelers should be able to provide their mundane cousins with magical gear that helps them in more different roles than "Ring Bearer" and "Magical Meat Shield". Hopefully some magical robes are good enough to have some "mage" champions using them instead of the usual heavy armour?
Which reminds me: that purple staff at character creation? If I pick it, I never use any other weapon for my Sovereign. Best 1 point ever?
"Champions aren't being nerfed as much as things are being balanced around them. The most significant direct change to champions is that injuries matter more. If you have a champion with 6-7 injuries on him he will be severely handicapped, it may be time to hand his equipment over to a promising newcomer without the battle scars. XP is divided by the members of group to make it less rewarding to steamroll the map with your stack of super heroes."
Considering that Champions can be killed by monsters (or were?) and enemy AIs, that their number is limited (no Dynasty and/or champion recruiting events) and that now they could end being not so usefull if you don't care about their health: do we get some kind of "Retire Champion" option? It could be something like "You lose this Champion but get a random level 1 new one". Or maybe you must select a city and he cannot be moved from there (can defend it) but provides bonuses to the city based in his Path(s). I only see the AI suffering from crippled Champions anyway (load/savers won't suffer it and careful players only if unlucky?).
"But the big changes are in dramatically decreasing the tech costs. There were always good units to make, but if your champions were level 7-8 by the time you got to them then it didn't matter. Now your trained units are better, come earlier and mean more."
Some more speed in the default research pace is not bad but... dramatically decreasing costs? My issue has been more with the placement of some techs (or the existance of some), like those archers that by the time I can research them, they have no place for them in my main army. But yeah, maybe it's tech cost matter too.
