I've been playing Civ4 again since I bought the complete edition on Steam, but I've also been jumping back on Civ5 just to sort of do my own comparison.
The thing about Civ5 that seems to bother me the most besides all the faults you guys have listed, is that you pretty much cannot really achieve any other victory besides war. I tried a culture game, but the AI civs are so erratic in behavior. I was on good terms with everyone, and for a random reason, my friendliest Civ declared war on me, and I had no indication prior that he was pissed off at anything. It's just a start of a turn and bam, his military is surrounding my borders. WTF.
To reiterate, the AI is so freaking random, and their behavior is unpredictable and completely independent on what you do to be friends with them. I had a Civ denounced me at the start of a turn when in the previous turn I gave him some luxury resources...Another explanation would be that the AIs were programmed to be the biggest assholes.