How about to change a combat. When you engage the combat you get (optional) real time battle with hundreds/thousands units - just like in Rome Total War.
A option to enter the city would be nice. Full 3D view of the city, with unique (random) placement of the buildings, people going around, etc.
I would take this one further: if you conquer a city, why not a "plunder mode" phase where you basically get to run wild in it, not unlike Grand Theft Auto but with era-appropriate look and feel? After all, you just spent an hour and a half besieging Rome, and when you finally take it, what, you get a few shouts? There needs to be more payoff.
Other wish list items:
1) Bring back Civ2's tile transform ability for modern workers. Israel used to be a desert but it's not today. That's how it's done.
2) Siege units should NOT be "suicide troops" in game play. That was never how they were used in any real battles in history. Their attack should be similar to how air unit attacks are done, just with a 1 tile range. They should NOT take any damage when attacking, but of course they can't obliterate their target on bombardment either. And the current rules about flanking damage would of course still apply to them.
3) More medieval siege units:
a. Battering Ram. Much cheaper than catapult, but can only wear down city defenses, cannot attack units. Requires Bronze Working.
b. Siege Tower. Each one allows 1 other unit to attack ignoring the effect of city walls/castles. Requires Engineering.
c. Change to trebuchets: attack +50% vs. FORTIFIED units, regardless of whether they're within a city, a fort, or just hunkering down in a forest. Should require Machinery.
d. Scorpion: somewhat cheaper than catapults, cannot bombard city walls. Requires Construction (same as cats).
e. Bombard: early cannon. Base strength 8, similar in bonuses and vulnerabilities as cannon. Requires Gunpowder.
f. Petard: gunpowder bomb, used for wearing down city defenses. Bombardment consumes unit (similar to guided missile). Should be cheap. Requires Gunpowder.
4) More UUs, preferably 1 for each age for each civ.
5) 1 unique wonder per civ.
6) More "canned" earth scenarios, and earth map related options.
7) Leaderheads per era (e.g., show Montezuma in a suit if he is still around in modern times!)
8) More resources, e.g., tobacco, cotton, etc.
9) Basically take a look at what people are MODDING and get a CLUE from it: they're modding what people want, so glean ideas from it for Civ5.
