"Civ 5 is the only game in the series I've played. How is it more simplistic than 4?"
It's been a good long while since I've played 5, so perhaps I'm not remembering correctly, but I recall the amount and complexity of data to have been notably less overall, and, from a strategic point of view, the player was capable of doing things that very obviously cut the corners of things which were supposed to be real barriers to have to work around: case in point, water is not even a barrier for land units, presumably because building transports would just be a boring hang-up against being able to casually invade without investing in a navy. That's just one example, but I think it's a good one to illustrate the change of intent with game design that I perceive. In 4, you would have to actually devote time and resources to building a fleet, and if you encountered water, it was a real prevention against movement in lieu of this. I'd have to reload the game and look at a lot of things fresh to make a carefully delineated list of this, but just about every facet of the game: espionage, diplomacy, warfare, etc., had more data inputs than 5. A brief glance at the UI menus for each game should confirm that unambiguously. I will be happy to concede that I'm wrong if I am, but that's how I remember it.
"I strongly agree with this. Fortunately, there are lots of mods out there that fix this. My mod, Fantastic Ancients, changes it to 3 per tile, but it also changes a lot of other stuff. There are some out there that change it specifically though, like this one:"
Yeah, and the one unit per tile thing is another strong example. While ostensibly it was supposed to make combat more interesting, it did still simplify the mechanics and often just resulted in awkward, unrealistic and clunky movements. That's cool that there are mods for 5 which work around this, though. I would agree that the stack of death in Civ 4 was unsatisfying, especially when only some very slight changes would have mitigated these problems considerably, but 1UPT was not the way to go. For instance, In vanilla Civ 4, siege weapons inflicted collateral damage on other units in the stack but were not able to kill them totally, but were often themselves fairly weak on their own, so it made the most logical sense to suicidally attack with siege weapons to soften up enemy units, suicidally sacrificing several of your siege weapons on the front lines so that your attacking force would be up against a weakened enemy, and this meant that stack compositions of 60-70% siege were ideal, and that they were supposed to be your front-line units. That always felt strange and silly, even though the promotions system and unit specialization in conjunction with a defender's bonus was itself satisfying. Realism Invictus used the core of the system but overhauled it, such that siege weapons begin with rams, not catapults, and are at first only useful in providing an aid bonus to a stack when attacking a city, and in reducing city defenses. Ranged attack doesn't even begin until bombards (early cannons are represented in the mod), these actually don't inflict collateral damage: instead, heavy cavalry does. So, the combat system with the mod is superb, IMO, but base Civ 4 did have a glaring problem here, but a fix along the lines of this could have been made for 5 and yet they went in a completely different direction, which seemed aimed at someone not keen or interested in a plausible model of military strategy.
"City maintenance? Are you talking about simply having a gold cost for your city? What kind of city maintenance did 4 have?
In any case, I disliked how 5's happiness system worked from the start, and how the whole game seemed to be biased against warfare. These were all issues I strove to fix with Fantastic Ancients."
Yes, there was a dual-faceted financial check on expansion, contingent upon a few factors: number of cities overall, and then each city's individual distance to your capital (which can be moved by building a palace in another city, if need be), and then courthouses reduce this further. If you take the State Property civic, it eliminates the maintenance cost from distance to palace, and there is a national wonder (i.e., one that everyone can individually build, but still expensive), the Forbidden Palace, which acts like a regular palace in this respect. This makes plausible sense as a check to expansion, even if this mechanic is pretty simple, in representing the administrative costs of an empire. (It also correlates to civic maintenance, for the same reasons.) In RI, additional cities also directly contribute to technology cost, as a further check on expansion, which was a good change since the runaway civs always became impossible to compete with research-wise, and now you can feasibly play a tall game, if you so choose. There does need to be a system in place which prevents casual expansion, but happiness does not make sense at all. In fact, the way that 5 modeled it, almost made it seem like your people frown upon their own civilization thriving: why would people in a small city on the outskirts of an empire be equally (or at all) affected by the capital city increasing by one population point? Again, I think the developers just wanted more shiny flare in the game than to have designed a historically believable and well-functioning mechanic.
"I'm very curious what you mean by this. Wars in Civ 5 sometimes have to do with iron, oil, uranium . . ."
Actually, I will have to give the point to 5 about the resources. That one source of any resource is both permanent and infinite is one feature of 4 which is disappointing. In fact, if I could add any one major feature to the game, it would be some kind of a rough approximation of modern finance, but it's just not in the game. They flirted with it with corporations, which were fun, and made it such that the more of any one kind of resource that you controlled, the more output each respective corporation yielded (and corporations themselves behaved like a modern, secular analogue to religion in that they spread and you are incentivized to promote this), but it stopped short of something like representing a national debt or a system of credit, which would have been really enjoyable even if it was made rudimentary. Realism Invictus scrapped corporations because the modders didn't like it, but there is now a multi-tier industrial system, where certain resources are manufactured into finished goods, and you must control multiple instances of a base resource to retain its benefit in addition to your supply chain, as trading away a resource eliminates it from your use. That is a fun and interesting, but still doesn't satisfy what I'd like to see. In any case, it's already a fantastic and dynamic game. You can't have everything.
Regarding geography (sans resources, as I'll give you that), I just didn't see the same kinds of game-defining things like vast jungles or deserts, influencing play in the way that it does in 4, and, as stated, even water doesn't matter much for purposes of strategic movement or defense! This one I'd probably need to play a new game of 5 to get a fresh take on, however.
"How did Realism Invictus do it? I do remember somewhere seeing a mod for revolutions in Civ 5, probably this one:"
To the best of my knowledge, they literally just incorporated that mod within Realism Invictus directly, although this one was Revolutions for 4. I really, really like what it adds, as that would have been the most glaring thing missing, were it to left out. Basically, all cities have a separatism level whose inputs are contingent upon the "global era" which is the average era of all civs in the game, rounded down, and as you progress through them, separatism becomes harder and harder to quell. It is opposed by the size of the garrison, espionage and government type actions. Cities can secede, and even conquered civs can snap back to existence if their conqueror can't hold onto them or supplant the latent culture well enoughl. Now there is a real system of domestic stability which adds so much to the game. While the AI isn't great at managing it, as the player it really does add to difficulty. You can't even settle ungarrisoned cities without revolt risk.
It's pretty complex, but you might really enjoy Civ 4: RI, given some of the things you've agreed with here.