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.