1.) Best aspects of diplomacy:
- Lots of options. Sharing maps, pacts to share research/wealth production, trade pacts, United Planets votes (aka voting with you in next council), etc. I want to be able to make a lot of different diplomatic offers, including treaties, trades, and gifts/requests/tribute.
- Europa Universalis has a very large +200/-200 relations rating, that prevents the AI from randomly betraying you; I don't understand why no one else has done this. The relations rating goes up/down based both on major/minor events (up to +/- 100) and on a monthly (aka turn) basis bringing it up or down by a modest amount (assuming you didn't bribe them into liking you, in which case it could go down very fast).
- Logical vassals/protectorates. Nations that are afraid of being conquered by their neighbors or are simply ineffective on the grand scale should be willing to or even offer to become a protectorate of another nation. A nation might join either a faction it is afraid of, or a rival of said faction (or simply another powerful nation they prefer being subject to), based on the circumstances of each incidence. Civ4 and the Europa Universalis series make the most sense implementing this feature.
- Nations should be willing to make peace if they are getting destroyed in a war; just because their military is 5 times bigger than yours doesn't mean its 5 times better, and I get frustrated by games where I consistently beat an AI but can't make peace (GalCiv2 and Total War come to mind). They should also remember that you crushed them last time you fought (or that they crushed you).
- You should be able to form temporary alliances between multiple factions, for the purpose of rivalling another faction or alliance. Europa Universalis II did this feature (without any goal for the alliance though), and balanced it by simply having the alliance dissolve if no one in it fought for too long. The problems with this feature though, are that it is admittedly based on having larger numbers of factions (minor races should be included in this consideration) and that in EU2 alliances often formed too often and too quickly (and you couldn't get an ally back into your little coalition if he joined another grand alliance).
- I HATED Civilization 5's diplomacy, for a few reasons. First, declarations of friendship built pseudo-alliances that made playing with 20+ civilizations impossible; when one or two friends denounced one nation, the rest would all start following suit regardless of their relations to those two. I even had to deal with a nation that I liberated back into existence denouncing me in one game. Second, warmongering penalties were abominably severe, and NEVER WENT AWAY; Persia still hated the Greeks in the 21st Century because Alexander the Great tried to obliterate them millenia earlier. Third, the AI was still fundamentally stupid; a nation with no friends wouldn't be any more eager to make new ones than a nation with 12 allies, and on the other hand a small and militarily-backwards nation would eagerly provoke a war with a far larger and more powerful nation with more allies, on the grounds of something ridiculous like a minor border dispute. To be blunt, I don't understand how so many people promote that game's diplomacy setup, as I preferred Civ4's diplomacy far more (not to mention GalCiv2's); it was so bad that I can't really bring myself to play the game at all despite enjoying the other aspects of the game a lot.
2.) Turns in a game:
- Probably 300-500 turns. I rarely finish my games once they reach the mop-up phase, although that's fine so long as the rest of the game is long, and entertaining. Games can go a lot longer if it feels like the nature and pace of the game are changing over time (such as in Civ4).
3.) Good and bad elements from 4X games:
- Endless Space has a really good UI, making everything easy to access and smoothing over the overall entry into the game. It helps a ton when a game has a clean, convenient, and easy-to-use and easy-to-read interface.
- Civilization 4 and Civilization 5 are great examples of shooting yourself in the foot during game design. Both games are basically fantastic (Civ5 only with the expansions though)...except that both games have something so broken that it's hard to bring yourself to play them. Civilization 5's diplomacy (in larger games) is appallingly bad, while Civilization 4 suffers from debilitating stacks of doom and fundamentally strange combat (why are catapults suiciding themselves in combat, and why are helicopter gunships vulnerable to longbowmen?). No matter how good the rest of the game is, you can't break something essential like combat or diplomacy.
Note large Civ5 rant from above for more details.
- The most frustrating thing about most 4X games is the colony rush; some games, like Endless Space, do a really good job of limiting your ability to expand (given a large enough map), but otherwise the game is often decided by the map dumping too many good planets close to one player, or for a player happening upon a good planet before his rival can reach it. Civilizations games have a logical counter to expanding too fast, but the AI doesn't seem to care and rushes anyways (meaning you get less territory, while the AI's growth is stunted to greater detriment). The only way to counter overcolonizing AI is to be militantly-aggressive.
- I hate it when culture mechanics are arbitrary. If the peace-loving Altarians are overrun by Drengin culture while they are at war, their planets shouldn't defect unless they were conquered from another empire's culture. That culture should also be assimilated over time, resulting in closer affinity to your own culture. The values of a faction should greatly impact what factions they are able to culturally-defect to, not to mention aspects such as approval, loyalty structures, and garrisons affecting that chance. Civ3 had the most frustrating examples of these, where cities would defect right after you conquered them, while you were still at war.
- Another thing that drives me nuts in 4X games is when there is too much of a tradeoff in military vs territory production (buildings vs units). I don't like having to entirely halt civic production in order to build a military and falling behind AIs still in peacetime, or alternatively being perpetually vulnerable to attack while my aggressive rival becomes technologically-stunted. There need to be ways to build units without ceasing your territory's development (aka drafting units, building militias, hiring mercenaries, etc).