It takes too damned long to build anything. You have to essentially decide between building units or making improvements. You can't decide to pump out some military units then turn to Wonder Building or improving your city while those units are out conquering. By the time you build a sizable army you may have already made them obosolete by making some new advances. Ugh. Why does my whole BC era have to be taken up building a few items?
This + 1 unit per tile + crippling maintenance is supposed to cap you at having a relatively small military or risk spiraling into economic collapse. I'm not sure if I like it or not yet, but it's definitely not something that happened by accident. If you have a significant enough economy, you can be stockpiling gold (assuming you're not going for cultural win in which case 90% of your money will be going to bribe city states) with no significant military and then simply purchase what you need as you need it. If you have coastal cities you can save maintenance on roads by trade networking your cities with harbors and preserving roads / rails for vital military routes.
Gold is much more valuable now than in any past Civ game. Also, upgrading isn't too costly, and if you went down the right hand side (from memory) of the Honor branch, you get big savings on keeping your military modernized if you absolutely must have a standing army. The disadvantage to not having one is mainly diplomatic, but don't worry, even on Immortal/Deity difficulty Combat is pathetically easy and the only thing that makes the A.I. hard is the ludicrous tech / resources advantage they get.
Second, there is a dumbing down going on here that it is a little annoying. Everything seems hidden as if the designers are actively discouraging you from looking under the hood
The worst of it is that some things, like how maintenance is calculated, how much units cost, how maintenance scales over ages, what roads will cost to upkeep etc is all completely hidden from view. There is no documentatino, and all the encyclopedia tells you is that "roads cost maintenance" and "units cost maintenance". Some people are reporting that it only calculates maintenance every SECOND unit you have, so for each one you build you get one 'free'. Other people are reporting that it changes every unit... nobody can really tell wtf is going on.
It's kind of fucking important to understand how the game works if you want to be able to play it the best you can. I don't object to having it hidden from casual view with tooltips and stuff, but it's BS that it's NOWHERE in the game to be found.
Also maintenance. Jeez it just cripples you economically unless you spam the trading post and focus on some Commerce Civics. Why is my fully kitted city killing my economy far worse than my army is?
Trading post spam is arguably worse than mine spam from Civ 3 because your entire civilization is covered in circuses, which now that I think about it is actually quite appropriate.
For me, the most disappointing aspect of Civ5 is the diplomacy component. Unless I'm at war with them, I can't seem to tell how other leaders think of me.
They permanently hate you unless your army is huge (and thus your economy is going to be shit) and you are also nice to them. Otherwise they randomly come up to you and say stuff like "oh, hey, I always love visits from my favorite city state!" and "Your army isn't very strong. Wouldn't it be a shame if somebody decided to wipe you out."
Kind of a fucking tip off.
I've always suspected irrational AI's diplomatically are just an excuse for sloppy AI coding.
The A.I. is very sloppy. They claim that it generates a bunch of outcomes and then picks suboptimal ones on lwoer difficulty, and I believe that. Unfortunately, the "best ones" they pick on higher difficulties are not that great in many cases to begin with, so on low difficulties they're doing hilariously awful shit like moving workers into enemy territory, leaving archers exposed to melee attacks at the front of their ranks, fialing to use chokepoints successfully etc...
They are also cheese eating surrender monkeys. Alexander declared war on me, and 20 turns later I had rush bought 4x longswordsmen (he still had regular swordsmen) and some knights, took one fringe city, and suddenly he offered surrender with 5 cities (everything except capital!), all of his strategic and luxury resources and 200 gold.
Shit a brick. It's like the A.I. in GalCiv 2 where if you infalte your military points somehow, everybody starts just bribing you and accepting ridiculous extortion during war time to get peace. FIGHT FOR YOUR HOMES DAMMIT.