Sorry but the people who complain about CIV 5, complained about CIV 4, after done some digging into the forums!
IMHO I find CIV 5 better than CIV 4. It's more complex than CIV 4 and people who complain about "dumbing" down haven't touch the surface. Civics are more complex (Social Policies now) and building a big empire is a feat on it's own which was dead easy on CIV4.
Also in CIV 4 when you had an Iron mine, you mass produce Swordsmen, and here we go. Now you barely can make 3 if you plan to get the mandatory 2-3 catapults on a 6 iron mine (if lucky). So you have to fill up the gaps with lesser troops. And taking enemy cities to obtain more iron, cripples your empire beyond repair.
The AI has issues, but I hope that it will be fixed. (Try to turn on random personalities, they seem way smarter on Immortal and Deity).
So what's missing? Religion? Spies? Corporations? The last two came with BTS. Religion, come on was so overpowered that everyone was winning games because of it.
Was never bothered about it and the game was more challenging but many dropped their games when they lost the race.
Even on multi, how many multiplayer games were ruined because someone lost the early religions and stop passing the turn around? Not talking about single games which rate would be higher.
Seeing CIV 5 also on 3D on Saturday, seems I need to budget myself and buy a 3d monitor, replacing my 5850 with an Nvidia card
It looks AWESOME.