0. Mods must be sleeping. Usually a thread that kicks off with an insult to lots of people at once gets some love.
1. Civ IV costs the same amount as almost all other PC games. It's rare that I pay more or less than $50 for a (brand new) new PC game. After a few months or if I catch some kind of wierd sale (Fry's has em sometimes) I might get it for $10 less or so.
2. I think you'd need to indicate what choices are missing, because to me all the important choices are there and in addition you get way more choices over map creation, particularly for some of the more interesting map scripts (and there are way more of those too in general). My only beef is that it doesn't "remember" which profile you play under or settings you choose for any given game startup path - minor issues that I'd imagine will be changed. Maybe there are some game variants that I can't remember from Civ3/C3C missing. But I can tell you that being able to play a game with custom continents, specifying how many continents I want, or playing a specific type of pangea map makes me much more happy than things I don't even remember.
3. Civ IV doesn't take long to load or run on my machine. Civ is a new game. If you have an ancient computer it kinda stands to reason that new games in general aren't going to run that well on it. I see no reason for any game dev to cater to the hardware of 5 years ago. Why should they limit themselves that way? <shrug>
4. Civ IV feels like a great step in the evolution of the series to me. Civ3/C3C had a lot of problems with exploitable AI and limited strategy. Figuring out OCS (optimal city spacing) and executing ICS (infinite city sprawl) every game isn't my cup of tea. There's a fine art to it to be sure, but I don't think that's what the devs had in mind. I enjoyed the heck out of Civ3/C3C - but I think Civ IV is superior.
Civ IV isn't perfect, but there are far fewer ways to cheese the AI (especially via diplomacy), AIs are generally better behaved (particularly in diplomacy) your decisions have way more impact in general, and many aspects of the game are significantly improved, IMO.
The civcs system is superior to limited govt choices, religion is a nice twist, unit promotions give you a huge amount of options and make you value unit preservation more, leader traits are better than previous civ traits, graphics (opinion) are vastly superior, health and happiness systems crush corruption system, map generation is vastly improved, there are several different and legitimate ways to kick off your empire (chop build, various "first unit builds", going for religion or not, early rush (not immediate but you can still fight very early), terrain improvements are better (and railroads aren't ridiculous anymore), and more.
I like the way siege works. It's a hassle, but to me it represents the cost of siege. You need to bring a ton of it for a prolonged battle if your're going to burn it up doing collateral damage or you need to replenish as you go - either way you have to compensate for the mass destruction and ease of slaughter that collateral damage gives you.