I think that other then the 1UPT rule (which I like but it won't work on the Earth maps), Civ5 is naturally better for RFC. WHen the tools come out, maps can get huge (I've heard there isn't a fixed restriction), culture makes more sense in a historical view (not jst expanding ina circle), encampent improve barbs, city states could (not nessacrily wil) replace independents, and hexagons make a more natural world maps. Plus the incentive for having a small empire are there, so Siam could actually be strong.
I don't really like Civ4's created maps; I ony really played RFC and RFC modmods after a certian point. Civ5 is much more fun when starting in a random map, and it creates more realistic ones too. You know the changes Rhye made to ther mpa script regarding deserts and mountians? Civ5 comes with that. You get hilly areas, plains, big deserts. SOmething I haven't seen a lot of people notice, the map generator is a lot better. ONe game with Greece I started in a plain, with a river. To my immediate west and east was more plain, south was wtlands and the wet INdia, and There was a desert with my river cutting through it. ANother desert was a fair bt east, and North was grassland and mountain.
The game is a bit slow and buggy, I'll admit, but most of the complaints I've seen are just things they added in Civ4 aren't in Civ5, and realism things which I honestly dont care about. The economy is much better: gold is now used for upgrades, diplomacy, purchasing, city staes relations (give them money, they give you stuff), maintence. Reasearch is nnow based on population and buildings.
Complaints about complexity make even more pissed off: complexity doesn't always make a better game. Not to mention Civ5 has much more tactical depth, and culture, gold, and policies are more complex. hey simplified some areas, and made other areas more complex. Plus, other civs war agaist each other better, and you aren't forced to expand to compete in the harder difficulties.
AP, maybe try playing on King or higher, then I'll listen to your complaints about difficulty. CIv5 isn't for everyone, and the people who cliam Firaxis ripped them off are being foolish: they made a new game, different from Civ cottage spam and REX the sword 4. They were very upfront about how the game works.