I'll break this down into sections I believe are appropriate for the game:

Character Creation:

The weapons need to be more obvious in character creation, like this first thing you see when you switch to "appearance". My first character was weaponless as a result of me glossing over the appearances and this didn't fare well. Also, the design costs for weapons need a serious revamp downward. A club is 5 points... really? It apparently took a lot to find anything resembling a simple stick during the cataclysm.

As has been repeated infinitely since the beginning, you need more races. Stardock's customers have been clamoring for this from the beginning and not listening to your customers tell you what you don't want to hear isn't working out as a strategy now.

Economy & Resources:

No surprise, it is boring. As I predicted (I told you so) way back in beta 1 when the decision was made to ignore heaps of solicited beta tester feedback, the global resource system is uninspiring. The game is getting more praise in reviews for game systems that don't even work properly than the economy of the game is. This is a strategy game, and yet there are hardly any tactical choices to be made in trade agreements, city placement, etc. This is further hampered by the tech and diplomacy techs always placing new resources in your existing city influence areas rather than making you go out and either capture territory or pioneer it.

The different environments don't have enough effect on the game. Forest, tundra, desert, hills, etc... so what? They have no effect on resources or combat. Forests should restrict the range and/or accuracy of ranged attacks. Fire spells should be amplified by forests, earth spells by hills, cold spells by tundra, and air spells by desert sands. Some monsters and resources should be terrain specific. Regular lumbermills need to be brought back.

I really don't care for the "wander around and find" system of acquiring heroes. This works okay in the early game, but why aren't adventures for me to hire frequenting my pubs and inns the way they do in roleplaying games? Heroes should be attracted to a sovereign in mid and late game rather than just wandering around to be bribed. Some might go to the sovereign with the most influence, the most good/evil, the most spell research, warfare research, or put their services out to the highest bidder (Richest).

I'm still very much of the opinion that the game was way better back before global resources were implemented when city placement was a tactical choice that mattered a lot and you worked at building a trading empire.

Magic:

The magic tech tree is rather lackluster. Magic crystal resources are also too rare. How about being able to research spellbooks at high levels that give you access to new spells (such as research the fire spell book if you didn't take it)? Maybe needing to research a magic level to get advanced spell research levels? Research more impressive magical enchantments? Magical gear for mage heroes? Definitely give earlier and better ways of regenerating magic. Perhaps mana restoring potions similar to the healing potions?

Diplomacy/Dynasty:

Like the magic system this needs some work. You should be able to view other kingdom's & empire's dynasties without having to make a proposal. I'd like to easily compare the benefits of each arranged marriage. Maybe some way (spy tech?) of researching prospective spouses for your children and grandchildren? The children need significant boosts to the bonuses they give as right now they've all been pathetic weaklings.

The "Third Race" pathway of technologies needs a lot more life breathed into it. Make each one its own tech path perhaps that can be upgraded with new unit types. They're useful and a bare bones disappointment that should have had a lot more work put into them.

Combat/Warfare:

Warfare in Elemental isn't really tactical or strategic. There are lots of options here. Is it time to revisit the old damage types discussions? Have special effects similar to MoM (First Strike, Flying, etc). The terrain you fight on should make a difference. If you can't get cover in the desert and I have wind magic, I should always want to fight you in the desert. If I have strongly melee units and can set fire to the forest, then no archers and a bunch of Drath backed up with fire mages sounds good.

What choices should I be making in combat?

Overall: The beta testing process

I dropped out of active participation at the end of beta 1 because Stardock wasn't able to handle constructive criticism. They did a great job in beta acting on bug reports and incorporating our suggestions. But when Stardock was told something they didn't want to hear they stuck their head in the proverbial sand. I participated in the Twilight of the Arnor beta and it went smoothly and head an excellent launch. There also weren't controversial core game mechanics or any massive stumbling blocks like Elemental had. Stardock and Frogboy need to work on ways to sort for negative feedback (Yes, I realize this can be hard on the internet as most of it is far from constructive) because even though some things might not be what you want (more races playable at start) they are clearly in your best interest as a large segment of the customer base wants and expects those things.