Well here's my idea about it:
1) It should be simple enough to play a 10 year old could start playing immediately with just a little coaching. My 10 year old son loved MOM and still plays it even today. It was really his first pc wargame he ever played. Now he plays it on easy or normal all the time because he likes all the easy goodies he gets out of the crypts and dungeons and caves and the easy leaders that want to join him. I can still see that cheshire catlike grin on his face as he used to play it and go into those batttles.
2) The battles themselves should be quick and simple yet complex enough that a more mature player could find challenge and fun out of them based on difficulty of course. MOM has such a simple combat engine but challenge enough from the almost perfect balance of non-balanced troups. At least some battles should scare the player. I don't know how many times I had to run around for 25 turns to save myself and my city or that particular leader/unit.. 
Yeah I know what was one of the gamey tactics in MOM that should have been patched out. I never really did care for it, but, welp I just said if you can't beat the join them. In Elemental I would hope there are exit arrows for all the combatants. If I had to gripe about MOM that would be the feature I'd gripe about is the defender could only get out of the battle by running around for 25 turns and surviving. It just made those battles long and tedious.
3) The world vs you complex: MOM had this and did it very well especially if you played a Death wizard. Nothing upsets me more in these other wannabe's when the ai continously attacks itself and I'm winning the scenario. This comes to the overcoming the odds feature of MOM. All the AI's once a player gets ahead of them by say 10 cities or nodes should automatically ally and go after the player. All my games of MOM I got this kind of action and once again that's another element that made it fun and great.
4) Fun surprises in those caves, crypts and dungeons. It was always an excitement wondering what the prize was going to be after a tough battle in these caves, crypts and dungeons. Lol sometimes it was craptastic and most times it was pretty neat stuff and what was also great about it is that what you got was also based on the DIFFICULTY of the game. So, the higher difficulty you played the less you got. I loved that part. If I'm wanting a tougher challenge the last thing I want to get is the "sword of everslaying" after defeating a handful of zombies. But, if you played the easy game a lot of times that's what you got. Great for kids and great for experienced wargamers who want challenge.
5) Which brings us to number five. All the elements must be so great that a 10 year old will love it as well as an experienced wargamer. Now that's a feat no other fantasy wargame out there can compete with MOM with. It's really in putting enough difficulty levels and barriers in the game for the experienced player. Finding the perfect balance of power(s) in an imperfect world and allowing the player(s) to experience a world of their own and no two games ever being the same. Having cost and upkeep be so perfect that the player can never really overwhelm the ai easily.
6) This is something I would add to MOM just to make it more challenging. The futher you are away from your own territory the more it costs for upkeep and control of your units and summoned units. I recently played a little game called "Conquest":Medieval Realms and I was overwhelmed with the way supply works in this game and how a losing player can defeat the winning player if he just works and attacks that supply line. If the supply line is broken the other players loses ALL units in front of the break. What a wonderful little game this is. I would like to see more supply line rules in Elemental to almost if not this point that out of supply out of units in front of the break.
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and tear ducts! 
