I want Civ 4.5. Select features from 4 and from 5, with a pinch of Alpha Centauri.

From 5:
*Hex map and world generator - best civ maps I've seen by a long way.
*Combat system.
*Gold/research split instead of the slider.
*Ability to upgrade units for a reasonable price.
*AI which can't magically tell what military you have, and can be fooled by FOW and unit placement.
*Game pacing: early game lasts longer, late game is less tedious, units don't become obsolete on their way to their first battle.
*No road/railroad spam.
*Viability and strength of small empires.
*Cities can defend themselves against weak forces so no need for garrisons.
*Gold is useful and there's a lot of ways to spend it.
*Legendary start mode for resources. Mmmmmm, tasty.
*Weakened resource hammer/food/gold output means that city placement now calls for consideration of wider factors.

From 4:
*DIPLOMACY!!!!
*AI which isn't as dumb as a rock after a series of sleepless nights.
*Transparency on mechanics. You know why your unit upkeep is costing you that much, etc.
*Detailed breakdown of player/AI status: score, techs, cities - the works. I want to know where I am and where they are.
*AI leaders with personality.
*Leader screens which don't take ages to load and drag me out away from the game screen.
*The flexibility of the civic system.
*Religion.
*Wider range of resources, more 'use' from food resources.
*I want my end game summary window thingy back!
*The full collection of civs and leaders.
*Traits. The single, solid unique ability given by 5 is unbalanced, inflexible and not so fun.
*Great people construct buildings inside the city, not on a tile outside.
*Sense of awe.
*Big, fat paper manual filled with useful reference tables and info.
*Wide range of options for things like worker automation, etc.

To work on from both:
*A tech tree where every option feels useful and there are no filer techs a la 5 but where there's more options a la 4.
*Happiness. Global is nice and yet there's a few things about local I miss ... neither is fully satisfying.
*Wonders. I don't want an uber button. I don't want a boring building. I don't want some to be awesome and others to be weak.
*City states/minor civs. The idea is nice, the execution is always lacking.
*Culture victory. Booooring! Spam wonders and culture buildings, wait for points to pile up, win. Nice idea, now make it fun to do.
*Diplomatic victory. As above except chuck gold around, win.

From Alpha Centauri:
*Tech and wonder descriptions which don't make me hammer 'ok' in order to close the window and escape the tedious narration.
*This had the ultimate execution of faction personalities. Steal it - now!

Things I don't want to see unless they are massively changed because I've never found the implementation to be fun:
*Espionage
*Corporations
*City spam
*Large empires - make it doable in a way which doesn't weaken small empires. Make it function as a choice, not a min/max sum.
*Social policies. Too one-way and inflexible, I always end up choosing the same things, not exciting to use.
*Corruption

Things were either 4 or 5's version would be ok:
*Culture
*Unit promotions
*Unique units
*Barbarians, although I have a minor preference for 5's camps over 4's cities.