I am a huge fan of MoM... I will list a few features that I want Elemental to have and a few features that could fix weaknesses that MoM had.
Disclaimer: I have not bought Elemental yet, but I have been following it for a long time. Once it has a more complete set of features I will definitely buy it but I am content to wait for now. I have read a bunch of reviews, watched all the developer blog videos, and seen an in-game walkthrough so i am familiar with most or all of the game.
MoM had a great Wizard customization system and the races were unique enough that the combinations made it fun to replay over and over even though the actual game play was identical (randomly generated world, conquer your AI enemies).
Another great thing was the way unit enchantments worked. The fact that you could take a group of inexperienced spearmen that were worthless and make them into killing machines with the lionheart spells was really cool. I can see how this isn't crucial to overall strategy but its one of my favorite features.
The RPG progression system was WAY ahead of its time. In addition to having up to 6 heroes that had a mix of pre-determined and randomly generated attributes chosen from a long list, they would also have items that you could create yourself or find/buy. Furthermore, every non-magical unit in the game had experience points too and would gain significant bonuses from getting experience.
Finally, I really liked the tactical combat system in MoM. This is something I have little experience with in Elemantal but I would like for it to have the same ideas of moving your units so as to engage at the right time, keeping a protective formation, and being able to use spells to summon creatures, enchant units, attack enemies, and reshape the battlefield (walls, holes in the ground, smoke screens, etc).
Here are some things I read about Elemental that are promising to me:
The unit customization system seems awesome. This is something I always wanted in a strategy game, Empire Earth's wasn't compelling. If you can customize the following things with it, it would be amazing:
Choose from a large variety of weapons (long sword, short sword, 2 handed sword, lance, shield, bow & arrow, crossbow, axe)
Choose various qualities of materials (bronze, iron, steel, magical, mithril, etc)
Choose a mount (horse, wolf, tiger, giant eagle, elephant, chariot)
Choose various armor levels (cloth, leather, chain, scale, plate) and also add cloaks, capes, hats, coat of arms etc
Add special abilities to the units (Could be fire enchanted weapons, battle cries, healing spells, carrying poison antidotes into battle, knowing how to fight against cavalry, etc).
I think that the quest system is a good idea. It must have difficult challenges, varied objectives, and compelling rewards.
The city system looks like it might be better than MoMs. I suggest making it so that each city specializes in certain ways, economically and militarily. I also suggest a system where every city has a unique advantage, like allowing a special unit to be built or giving a bonus to units built there, or a multiplier to certain resource income. Also make sure that there is a strong trade bonus or alliance bonus from neighboring cities (minor cities) to give an alternate route to divide and conquer strategies.
Finally, one main thing that MoM did wrong was make it too easy to win if you went an extreme strategy. If you go all spellpower or all military its too easy in that game, in Elemental there should be trade-offs beyond if you can survive X turns then the game is a cakewalk. In fact, you should strive that the player must try to end the game or at least pressure opponents or else be completely outclassed after many turns have passed.