What part of this do you not understand?
"stacks of doom" (which is a very bad way to play Civ4 against a competent opponent and suboptimal against the AI unless necessary), and "the tactics!" (what, the tactics of spamming ridiculous ranged units and setting up a carpet of doom? there aren't much tactics in Civ5 except to brute force everything, except now you have to contend with the annoyance of ranged combat and micromanage a lot more units to get there).
That is a short summary of what 1UPT directly leads to with Civ5's city and empire management.
I've explained why 1UPT is bad over and over again, if you refuse to understand and respond to those in a reasonable manner and just call me stupid over and over again (which has been the entire argument basically), then there is no point in wasting time and energy re-writing, nor is there really a point in linking Shafer's autopsy of his own project which I presume most people here have read.
But hey, enjoy overpowered chariot archers and cbows making early war super super annoying. That this flaw was made worse in BNW just shows that Firaxis has lost touch with what makes a game strategically interesting. Obviously they want to save face and make the game into something more viable, but it's tough to backpedal on something structurally wrong with the game (and 1UPT is just part of it).
It never ceases to amaze me how many people tolerate bad game design that shouldn't be too hard to fix, because everyone who doesn't play Civ as their primary game that I've talked to thinks 1UPT sucks - in fact it's their PRIMARY gripe with Civilization V, the rest of the game's flaws could be patched over by the community but it's difficult to re-write core mechanics and AI to adapt to MUPT.
You can't really pick Civ4's as the sole example of why MUPT is bad, other games have implemented the SoD differently. I would prefer Civ1 and Civ2's mechanic of killing all units after the first defender is routed over what happens in Civ5, or Alpha Centauri's heavy collateral damage for routing a unit and AC's implementation of artillery. Besides, most of Civ4's problems come from stack killers and flank damage being really strong, city defenses being way too weak and trivialized by siege, and city raider turning cities into death traps. I already mentioned that building one giant SoD is a very suboptimal way to play against a human opponent for logistical reasons, but you do have to build stacks of substantial size and allocate troops efficiently. Another problem with Civ4 stacks (which exists in Civ5's carpet of doom too) is unit healing trivializing attrition as a means to damage stacks, and unit promos being generally too strong. I honestly think it would have been better to revert to Civ1/2's system of just having Veteran troops, or like AC and BE have multiple tiers of veterancy only. For healing, the best way to do that would be to only allow healing by re-supplying units, which means keeping a supply line intact. Whether to require manually moving units to the army, or have some means to abstract the supply line to something which doesn't require player book-keeping, is up to whoever designs the system.
Until then, I and many others find 1UPT terrible. Most people take one look at Civ5, dismiss it as awful, and sigh that a once-good series has been dumbed down to this. I'd rather have a Civ game that incorporates what Civ5 did right with hexes, patches over the fill-the-buckets nature of the game's economy, but most importantly makes it so war is not lame.
Really though, I think Civ5 was designed around the same principles of freemium online games - just use lots of flashing success messages to make the player feel like they're accomplishing something, encourage people to buy into DLC and exapnsions, and keep people addicted. Plenty of online games do something similar.
