CIV5 has killer graphics and a better combat system than its predecessor. however, here is my list of things that makes me believe CIV4 might still be at the top. and it's not getting better the more I play.
NO RELIGIONS: war is the face of religions (and capitalism). a lot of people are complaining that in CIV4, it just blocked diplomacy but I'm sorry, world leaders have to deal with it so why it shouldn't block diplomacy? i've been able to solve this problem with mass missionaries invasions before so... plus countries of the same faith are way more near each other and it's always been that way. there is no diplomacy points in CIV5 so what is the point to supress this aspect anyways? I agree that Firaxis probably wanted to give more freedom in relation-making but to this extent?
NO GOVERNMENTS: The social policies are OK but they could have been added to a government. we all now realize there is no more consideration about what would be best for you at a certain time
NO % GOLD/SCIENCE: not a big deal but in CIV 5 you can't halt your science for a few turns because you want to cash in to upgrade your units for an upcoming war. you have to think more in advance with your money so you have less moves that you can do in order to have quick gold.
NO SPANIARDS, NO ZULUS, NO INCAS, NO DUTCH, NO MONGOLIANS, and so forth...
NO SCENARIOS: ??????? Perhaps it will come with the expansions. hope so.
NO HOTSEAT: again, why? It was kind of complicated to play that way in CIV4 but at least we could. now with CIV5 you have to log on Steam that bugs you all the time with its adverts and of course, in these times of consumerism, you now need two computers if you want to play with a friend. BAD.
NO MAP EDITOR: this doesn't bother me that much but still we can't pretend CIV5 is very user-friendly unless you say it is less complicated. also, my feeling with CIV5 is that it's either on survival mode or you have a great domination game. nothing much in between so at least in CIV4, one could fix things up with the editor. in CIV5 you can't.
BAD ROAD-MAPPING AND PATH CALCULATION PROBLEMS: A lot of bugs. you have to click twice quite often to send something outhere for some reasons (ex. your ship has to come near another ship first and then you have to click again to attack it).
ANNOYING NOTICES: way too many.
CITY-STATES: an add-on that doesn't bring much to the game. they are literally useless except using them for their resources until you wipe them out or maybe as buffer states to protect you since you can give them units (you can't give units to other civilizations in CIV5). other than that, they bug you all the time with futile demands even if they are faaaar away.
Finally, AWFUL ARTIFICIAL-INTELLIGENCE: a competitor will give you half their territory if you kick his ass in battle but don't expect him to give you 10 gold even if you have riflemans pointing at him when he's sticked with medieval units. the computer doesn't really tries to win at all as a matter of fact.
I've played all Civilizations since age 10 and this one, in my opinion, is the last and the least of the last two... until patches patch it or expansions expansion it.