I will start out by saying Elemental is addictive. Even so, it has a rather large amount of minor to medium flaws that individually are fine but in unison gamebreaking. A few of the issues are also overlapping. Remember that all the solutions are just how I would solve the issues, they might not even completely solve the said issues but will atleast aleviate them.
Medium flaws:
1. Health is way too low for everything. Your soverign is basically a walking deathtrap with his low health, and in general health is too low until you become awesome enough to train a company of 12 elites.
Solution: Increase health by 3x, including health gains from constitution, remove 1/2 of defense and add a magic resistance stat that is given by everything with elementium and crystals in it.
2. Lack of caster items. Your soverign and champions have no acces to any caster gear except maybe a ring or a amulet. This is especially problematic later on.
Solution: Add caster items that are researched with the magic tech tree. Add two types of caster items, magi and battlemage. Battlemage gear would have more defense and magic resistance than would soverigns or champions in magi gear, but they would have longer between casts and less intellect and charisma.
3. Lack of usefulness of shards for non-magic soverigns. If you focus on a melee soverign you basically gimp yourself in this game. First he has low health, as per issue 1, secondly, once magic actually becomes useful shards will be awesome.
Solution: Allow shards to be imbued into units, champions or your soverign. This would expend the shard until the unit dies or the resource building is sacked by a monster/enemy, which would then kill the unit, and you would only be allowed one shard per unit, 2 per champion and 3 per soverign. Example: Air shards give +10% attack +20% combat speed speed +5% move, fire shards give +20% health +20% attack, water shards give +30% magic defense +10% attack +5% health, earth shards give +30% defense +25% attack -15% combat speed.
4. Overpoweredness of tech research. The benefits of tech research are much better than the ones for arcane research. I do not know if they were ever surposed to be balanced or anything but at the moment you basically focus on tech research as it has all the benefits.
Solution: First, increase the cost of each spell level by 2 and spells by 1.25. Secondly, allow casters to create resources with spells starting at spell level 6, and make it scale with intellect. Example: Fertilise the land. Spell level 6. 30 mana. No benefits from shards. Does a roll from 1-2000 then reduces the number by 2x intellect. A number from 1-20 is +6 food, 20-60 is +5, 60-240 +4, 240-500 +3, 500-1000 +2 and 1000-2000 is +1 food. At max spell level, allow the caster a low chance to create the one and only elememtium deposit.
Minor flaws:
1. No "huge" maps. I know they are possible since I have atleast seen a 14x14 map on the mod library, so they were likely disabled.
Solution: Enable them again, or if they were disabled because of performance reasons, enable them once, and if you can, you have fixed the performance issues.
2. Unable to change resource abundance from the map screen. This is not that important, but nonetheless a flaw.
Solution: Allow you to change resource abundance without modding. (Even changing resource rarity in the .xml files dosen't work, atleast not yet)
3. Lack of "end-game", technologies outside civ/imp tech tree. All the good end game stuff is in civ/imp and the likelyhood of "refined x" appearing is so low for the others that they are not worth it. You can basically go 10 warfare levels without seeing a single refined tech, while you coul have gotten 10 refined techs if you went for civilization instead.
Solution: Add refined health, giving +5% health, after researching elite troops, refined unit training, reducing training time by 5%, after researching the war college tech (And whatever the empire equivalent is etc), refined crystal production, +10% crystal production, after researching shard mastery etc etc. Basically add a refined technology to nearly every single possible stat, but add them all around in the different techs so they are about equally useful late game.