Not wanting to start a flaming, just trying to point out that not everything is as simple as you put it.
Mh, I think you calmly stated your opinions without throwing around flames. Let me see whether I can stay in the same vein while stating where our opinions differ.
1. religion
nice new aspect which is unfortunately too politically correct. Every religion is the same 100%. and at higher difficulties its often better not to adopt any in order not to make too many enemies. still a nice aspect overall
Agreed. One aspect that I like about religion is that it helps forming "blocks" of empires who like each other, but dislike other "blocks". This works similar to the "same culture" bonus of Civ3, but is a) stronger in effect, and b) plays more natural (in Civ3, you could have a positive diplomacy modifier with a civ far far away because on Earth your civs are neighbours - imho the religion system is a much more refined way for block building).
Making all religions equal forfeits lots of possibilities for strategical decisions, so I agree with you, the game would have been better if different religions had different features. Fortunately, modders are able to provide those.
2. diplomacy
CIV does have options like asking someone to fight someone else without getting involved, that's true. However, trading has been nerfed beyond recognition. Not gpt for techs, the beloved WFYBTA hardcoded limit, the redding out etc. Espionage is a complete joke. There is no way to make a comeback from behind via diplomacy in CIV.
Personally, I find trading much more realistic now. One of the things I really didn't like about Civ3 is how you could go tech-whoring, and how many games ended as mad tech races with every player trading every tech as soon as possible. Imho, the Civ3 AI was also much too gullible when it came down to trading cities. Trading has much improved imho.
I agree that Espionage in Civ4 isn't very useful. Personally, I don't miss it because I very rarely used it (it was a vastly overpowered feature in Civ2, and I cosciously decided not to use it because it made the game less fun for me - I honestly don't know whether and how it was implemented in Civ3, I only know that I never used it there). I can see how people who like this feature are disappointed from its implementation in Civ4 though.
Contrary to what you're stating, I've had several comebacks via diplomacy in Civ4. I've even had AI rivals helping me to come back by gifting me tech when I was backwards and they liked me (partly due to me adoptng their religion), which I found quite nice.
3. Tech tree
true, there are more techs but once you are a pro, you would know which techs you need to stay in the game...say writing, alphabet, literature (for GLib), then maybe CoL (you would know the techs the AI shuns and techs become not that flexible), later the rush for paper/edu and liberalism sped up by a GS etc
This is one possible way, but there are many others (CS slingshot being the most prominent one). Personally, I find myself choosing many different routes through the tech tree from game to game. Even if there are key technologies, I think it's safe to say that the Civ4 tech tree gives you more freedom for doing so, because the Civ3 tech tree had these hard-coded eras that blocked you from many advances unless you fulfilled a twelve-(or more)-part requirement.
4. Combat system
CIV's combat system is too simple, only 1 value for attack/defense and the headache of the promotion system. Yes, there is the paper/scissor/rock thing. But nothing beats an axe rush in the beginning. Plenty of catapult/cannons/trebs/artillery will do the job. I sometimes think you can win the game merely using atrillery.
Plus, it has become a chore to fight, not fun. WW is plain crazy without proper governments...AW gamers feel totally frustrated with CIV
The promotion system replaces (and vastly expands) the simple offense/defense system of previous civs, so there's no need for this any more. I find that it gives me a lot more freedom and opens many possibilities that I wouldn't have had in Civ3. I've lately come back from a bad start (no copper, no iron, no horses, aggressive neighbours) with offensively promoted archers (drill III and IV work nicely). I was not forced to turtle, Civ4 gave me a freedom of choices that I didn't have in a similar situation in Civ3.
Axe rushes in the beginning can be powerful, and were overpowered in the past, but can now properly be countered by chariots, which will simply smash most axemen they encounter.
The trebuchet may be too powerful as a city attacker, agreed. However, hearing from someone who prefers Civ3's combat that Civ4's artillery is too powerful sounds a little strange - actually, the one thing that I like most about Civ4's artillery is that it's much less powerful than its implementation in Civ3 Conquests, where artillery ruled the world, since it could red-line anything without any danger of being destroyed.
5. Graphics
Ueberfluessig wie ein Kropf would I say as a German. If there was ever a game that did not need 3D, it was this game. The mere fact of laggy play, crawling speed, small maps all boils down to this awful graphics engine that a civilization game doesn't need...
Here I agree with you. I wouldn't have lost anything if Civ4 had used the same graphics engine as Civ3. Fortunately, my machine allows me to play huge maps with 24 civilizations without lags, but it's really sad that so many Civ players around the world are forced to play smaller maps than they would want to because of the system requirements of a 3d engine they could happily do without.
one thing though, that was indeed simpler, is modding and that's the big plus of C3C...
Simpler, yes. The Civ3 editor was much easier to access than Civ4's python, XML, and SDK. But Civ3 modding, while being easier, is also more limited. A mod like Blake's Better AI, which improves the game AI a lot, unfortunately will never be possible for Civ3.
All in good fun.
I'm still not bored, I'm still playing, fortunately by finishing the game twice on Emperor and usually winning on Monarch without reloading I'm somewhat cured - now I can play other games as well. 
