So, with the addition of the new city building system, I think that the amount of content that the game has is almost sufficient. The current content is meaty and provides a good random element to the game; however, there is one final big system that I think that the developers should implement:

Random events.

There has been some talk about these in the Beta 4 thread. I think that this is the last major system that the game needs before release. They can be simple events, but two major events are desperately needed: 

1. Champion spawning events

2. Monster/goodie-hut spawning events

Here is why: Currently the mid-game suffers from a tiny bit of malaise unless you are at war with another faction. By season 100, you have cleared out most "goodie-huts" and the spawned champions around the map have been recruited. At this time, the only thing to do is engage in city-building, army building or war. The quest system has stagnated (until you can build up your army) and exploration is hindered by the encroaching AI. 

The addition of new spawning champions/monsters could keep the player busy in this period while contributing to the player's power in a positive fashion. Just one word of caution: for the monster lair spawning quests, care should be taken to give the player an option to sacrifice gildar/mana/population in order to prevent the monster hut (similar to Fall from Heaven 2's system). This gives the choice to the player and reduces some of the random elements of such a system.

One final suggestion for random events: make most of them small increases in city stats or unit stats, but make them occur at a moderate frequency. I would say that 20 turns per event (obviously, at random) would be a good pace.

Some minor suggestions:

1. Include more summoning spells for the other magic branches.

2. Remove the "one-per-caster" restriction from the low-tier summon spells (this restriction could be kept on the higher level summons for balance purposes). I think this will allow magic-based players the ability to burn some mana and maintain a weak, but large army

3. Add one or two more unique buildings to the factions. Pariden's unique building is excellent and adds flavor to the nation.

And... that's it! I think that with all of these suggestions, you could content-lock the final beta, focus entirely on balance, and release one of the best 4X fantasy games in recent history. It's been a long road, but you guys have done an excellent job!