So, my experience with modmodmodmods
Rise from Erebus + Ashes of Erebus - meh. Added new civs and lots of additions and changes here and there. But there is no system to that, so changes are rarely to the good, and quite often to the bad. Gui is particularly crap. What's worse, AI is dumb. I have not see them fight with each other, they develop slowly, and one time I was declared on, enemy has not even bothered to send an army my way.
Master of Mana + Master of Mana Xtended 3 - great. Master of Magic meets Alpha Centauri. Very different economy, very different magic. Support spells (such as Blur) work as auras, so you only need to have a one adept per 6 or so troops to get full bonus of all support spells you have learned. Summoned units and priestlikes also have their own sets of auras. Town-buffing spells are global enchantments, that work like in MoM (lots of mana upfront, some mana for upkeep). Lots of terraforming spells. I was a little disappointed, though, that serious terraforming spells like earth->ocean is not working outside your borders. Also, city does not seem to became coastal when you sink a square besides it.
And what's especially good, is that AI is adequate. They expand, fight with each other, and can use doomstacks, even overseas. I had very annoying war with Svaltalfar - they have parked their doomstack just outside my borders and atacked on the same turn they declare. Just like I do
And if they see that one city is defended, they move to another and attack it instead.
Master of Mana 2.11 + Master of Mana Xtended 4.1 - very different from previous. Pretty much everything is overhauled, especially economy. In Xtended3 many buildings and improvements was giving special resources - lumber, herbs, stone and metal. They were mostly luxury stuff (not in game luxury meaning) - you could buff your units with them, rush building with stone etc. But in Xtended4 they are mandatory for most improvements and buildings. Also, improvements cost gold and resources to build too. Even farms costs a hefty sum of gold and stone now. So, most of time you can't build shit, because you don't have resources. It's quite annoying, but it makes game much more deep, and you have to think hard on each turn much earlier.
There are total of FOUR tech trees - standard scientific, magic earned with magresearch, religious learned with faith, and new one - cultural, learned with guess what.
On the minus side, AI seems to don't know how to think hard enough, so they do very poorly, compared to Ex3 or vanilla FFH2. On the other hand, barbarians are buffed through the roof. As a result, you have to train superhighlevel units to siege barbarian forts, and then you can just stomp with said superunits over any AI civ you meet. Funny thing is, one of my two superterminators is a measly Devout (Elohim scout), which was with me from the urn 1 and just has gradually grown to a monster she is now.
But even without AI doing anything, game is a very fun builder, and if you have fog of war anywhere on map you will keep finding there things to kill.
Some screens from 3.0
With auras, equipment, mutations and whatnot units tend to have tons of effects on them.
Dwarf attacked me from the sea. But they had no chance against endgame heroes and national units
And one from 4.1
Just to show how expensive building improvements is.