Sulla hits on most of the flaws in CiV; but his conclusion that 1 upt is the major factor is wrong. There are other factors, many small ones that just add up, like the barbarian galley that sinks a modern steel transport with its arrows, or unit that decides to travel all the way around the world to get to a tile two tiles away that is temporally blocked, or my personal favorite...You have large number units near my territory, when their Civ is half a world away.
Granted, 1 upt is flawed, particularly later in the game when you can afford many units; but given the choice of that, over the "stack of doom', I'll take the 1 upt. This is my personal preference, one shaped by the types of games I prefer to play.
My favorite game of all time is Panzer General 2, followed closely by SMACX, Civ 2, Civ 4 BTS, then AOE ROR. When CiV was announced, I was thrilled that some of my favorite games features where being added all in one game! I pre-ordered the collectors addition! I don't normally layout $100 bucks on any game, particularly so if I've not demoed it; but this is a Civ game, how bad could it be? We'll the bad is, very bad, and the good is just "Ok" or "Potentially Good" (with needed patches).
Don't throw the baby out with the bathwater...
I know a lot of Civ players like the 'Stack of Doom', I never hated it...just thought it was too unrealistic. I realize that Civ is not historically accurate, but it is based on real history, real civilizations, with their, for the most part, unique civilization traits. Thinking of history got me thinking one previous games I loved, and what made them work.
Don't reinvent the wheel, "borrow" the design!
PG2, addressed the 1 upt with a 100 unit limit, period, simple but effective. Modders built units like TD's (tank destroyers, self propelled anti tank guns) with attached infantry, slower than normal TD's, but could fight in cities and tackle entrenched units more effectively than normal TD's. This is also historically correct, armored units often moved with foot infantry intermixed.
So Civ could allow some unit types to stack. Stacking should have some benefits and drawbacks. A drawback would be a Knight on the same tile as a Swordsman, the Knight loses some power and movement as it cannot maneuver well when intermixed. Maybe mobility units like Knights and Tanks should not be able to stack with same unit types.
3 units per tile seems reasonable to me, and could be graphically represented without hovering over a tile to see what is in it.
Cities could also be allowed to garrison 1 to 10 units based on their size.
ICS - small civs vs large civs- unit promotions and support.
Small civs could be allowed better promotions to buy, to compete with massive armies of large civs.
PG2 also had a 'Deployment Feature', you could pre-purchase units and deploy them later if needed; Or later, if all your deployment tiles where occupied. The deployment concept would work great in Civ, think about it, you pre-purchase units, pay half the maintenance cost when "un-deployed", and deploy them when in need. Maybe you have to wait a few turns to 'Call up the Reserves", as well. There are many ways this could help avoid this: Carpet of doom
This may even help avoid some game crashes caused by rendering so many units.
PG2 has "Core Units" and "Auxiliary Units". In Civ this might work like so: Core units you control, and Aux units, you give long term orders to. Imagine you as the "Supreme Commander" are asked by your General in "Alpha sector what to do? It might go something like this: The General in Alpha sector asked you permission to attack advancing units. You get a list of options...Stay in a defensive position, recon out but do not initiate an attack, recon out and skirmish the advancing units, attack them! Of course this would be no fun currently, because the AI is brain dead.
SMAC is my favorite all-time Civ game, not because it's futuristic, but because it has fast turns and you mod your units in game. Imagine a Civ late game that takes just a few seconds between turns on a large map, and does not crash, well unless you've played SMAC, you would say it doesn't exist.
City governors where great, many, many options to set for them, basically you set them up and forget about them, and focus on your core production cities. Again, this speeds up the game, and one less thing that pops up for you to do that may cause a crash.
The in-game design workshop in SMACX was great! Very fast, clean and crash free! Imagine that! Basically you got predesigned units automatically, but can design units as the situation calls for...need cheap aunits for attack, defensive units, ships with AA guns, better movement or expensive units that have multiple enhancements, many features for units could be added.
Yes SMAC had its flaws, by mid game you where either obviously going to win easily or you had no chance, rarely a tough fight until the end of the game.
Civ 2 was great because it was the last game in Civ series that did not crash often from mid game on. And the AI actually used ships in Fleets rather than single unit kamikaze actions. For the record: my system runs any game, on the highest settings, for hours, without any crashes, except Civ V! Win7 Ult, dual Asus 450's in sli, i7 930 OC 21%, 12gb ram, dual Raptor hd in raid0.
Age of Empires Rise of Rome, AOE ROR was great because it was infinitely playable in multiplayer. Great games until the last tree on the map cut down. I played many, many hours of great online competition. The unit graphics where nice, even by today's Civ standards, the terrain was basic, but much better than the very ugly minimum civ settings. Crashes happened occasionally, but you could rejoin a game. Civ V multiplayer is a sham, a disgrace to the franchise, SMAC, ten years ago worked much better.
The handwriting is on the wall...
Sulla says he's seen game companies go down this road before, I've seen it too. Resting or just profiting on their laurels. It's time for Sid to step up and fix this game or go right to Civ 6. Civ is last great game of the Turn based genre, and the only one this "old boy" can use his wit on instead of my slower reaction times RTS games take.