Using Daft's list:
1. Game Playability: civ 5 is better because it is easier for new players to learn. When I first played civ 4, I lost to barbarians because I had no idea what the best approach was. However, perhaps civ 4 might win out once you get the handle of it. Much temperance and patience required to reach that level though (see combat as to why that is).
2. AI's capability to defeat a human player given similar game rules: The AI definitely is hard in civ 4, even on easier difficulties. For me, if I found a neighbouring civ, I had about 30-50 turns to prepare or die trying to defend. In civ 5, it is easier but gets harder in the form of AI bonuses over difficulty. Since I don't know what it's like playing hard difficulty on civ 4, perhaps you might find civ 4 more challenging once you get the hang of it.
3. Terrain NA, imo.
4. Resources civ 5 has more strategic resources. Civ 4 has more resources in general and the ordinary resources can be used for trade to improve health and such.
5. Uniqueness (units, buildings, abilities) civ 4 has narrower unit and building diversity than civ 5, which makes game look like rock-paper-scissors, especially when you see the combat system (see combat). However, civ 4 has greater use of ability combinations with multiple leaders for some civs. The leader characteristics can give you a choice as to what you want to prioritize early with your civ, whereas with civ 5 it is not as clear-cut.
6. Graphics - of course, winner is civ 5, but shouldn't be the basis for favouring civ 5 over civ 4.
7. Combat Here, the questions of comparing combat are these: Do you like luck (% chance of winning a complete kill fight) or skill (combat strength based and incomplete)? Less detail/basic or more detail/elaborate combat rules, bonuses and penalties? Convenient unit management (which makes AI coding easier and therefore they can be more competent, but MP could be fraught with early stacks of doom zergs) or unit formation (which confuses AI and they sometimes make silly mistakes, but MP makes things interesting)? Purely melee combat (with ranged only applying to bombarding cities) or balance of range and melee combat? If you prefer mostly the former, civ 4 is better. If latter, civ 5.
8. Terrain Improvements - pretty similar, however civ 4 has better gold-generating improvements which scale over time so long as they're used. Civ 5 has more diverse tile improvement with UIs and such.
9. Technologies- their number and intelligent setup (prerequisites and benefits they give) pretty similar, although I may have forgotten layout mostly for civ 4.
10 Generic Units - including req. tech, benefits pretty similar although if I recall with civ 4, you just need at least 1 source of iron to keep making swordsmen and such. Civ 4 also has a good rock-paper scissors mechanism where axemen beat non-cavalry, swordsmen are good against cities, spearmen beat cavalry and cavalry beat non-spearmen. However, those unit benefits become narrower over the eras. Civ 5 has a more clear-cut approach to units and their upgrades.
11. Generic Buildings pretty similar early on with granaries and libraries and such.
12 Unique Units- Civ 5
13. Unique Buildings - Civ 5
14 Unique Abilities - Civ 5, although civ 4 character abilities are nice for combinations.
15 Speech - Does this mean the interactive diplomacy menu with the way characters act and speak? The starting speech and end speech? The tech speechs and wonder speeches? Civ 4 makes diplomacy look rather undiplomatic but funny, with Catherine (or was it Izzy?) slapping you or Sumerian Gilgamesh picking you up or pulling you right up to his face when they refuse your offers or when Alexander gets into a fit of rage when he denounces you or something. In civ 5, the character actions aren't as dramatic.
As for the other questions, it's very similar and they both have nice quotes.
16 Graphics - you mentioned that twice, Daft.
17 Sound Effects - NA. Whenever I say NA I just think there isn't anything significant to compare.
18 Naval Transport: civ 4 has the inflexible but perhaps more realistic "land unit-to-transport unit" system. Civ 5 has the flexible "every land unit, even a helicopter has a boat" system.
19. Naval Supremacy civ 4 again has the rock-paper-scissor mechanism but the privateer concept is much cooler than civ 5, because they're literally privateers and you can't tell who they belong to but anyone can attack them. In civ 5, the privateer is just a melee unit than can capture over ships. As for navies in general, I'd prefer civ 5 given the ranged combat system and such.
20 Expansion-Settling - civ 4: each new city costs gpt and in turn it eats into your science that way. Happiness is local/specific. I might be wrong but I think this system favours wide expansion with great emphasis on city specialization.
civ 5: Happiness is global/general but each new city costs happiness, culture and, as of BNW, science. Tall approach, as of BNW, is preferable and city specialization isn't that great.
21. Exploration I've forgotten all the goodie hut benefits in civ 4, but I know some contained pop bonuses, gold, map and tech bonuses, just like civ 5. Exploration is more dangerous in civ 4 because barbs are wild animals (not a metaphor, they ARE wild animals) until 1500BC. In civ 5, barbs generally hang close to their camp and between the camp and other players and CS'.
22 Multiplayer Capability don't know about civ 4, but in civ 5 it is great. Not sure whether the loading issue still persists though in civ 5. Try and see if you can do a quick game in one sitting in civ 5.
23 Air Combat I know in civ 4, you can bombard cities to reduce their defence bonus, attacking units functioned like melee (please correct me there if I'm wrong) and you can pillage improvements with planes, unlike in civ 5. There is interception in both systems but my mind is hazy on how it works in civ 4. In civ 5, it is pretty straight-forward because planes are ranged units.
24 Nuclear War's importance - SP Gandhi is a curse in both civs in this area, apparently. Both civs emphasize its importance. Both have cool nuke visual effects.
25 Space Race's depth they're pretty much the same (correct me if I'm wrong)?
26 Victory Conditions civ 4: domination victory is not absolute and much easier in both objective and the combat system, cultural victory is pretty straight forward, getting 50,000 culture each in 3 cities, diplo victory is...same as civ 5??
civ 5: domination victory is harder (get all capitals), culture victory is harder and does involve a fair bit of strategy to achieve it. Diplo victory is dependent on CS'.
27 Technologies- again, repeated.
28 Trade civ 5 has physical trade routes and diplo trade, civ 4 just has diplo trade
29 Population Growth same, I think.
30 Population Happiness - see expansion.
31 Great People - pretty similar.
32 Religion - how does religion work in civ 4? The fact that founding a religion is tied to specific techs in civ 4 makes no logical sense, both fact-wise and gameplay-wise. And what benefits does religion bring? In civ 5, religion is straightforward and is independent from science, as it should be.
33 Great Leaders - more diversity in civ 4 with regard to characteristics.
34 Civilizations - civ 5 has more variety.
