Summary: I have loved, and played all of the civilizations since being 8 years old playing Civ 1 on my dads crappy old pc. Civ 3 was historically my favourite, and thought 4 was ok. There are various changes to Civilization 5, some of which are revolutionary, and this is why many people are shouting from the roof tops. I read one review that said: NO religion, NO great people... etc...
Summary: I bought this game from Steam (as it was on offer), and have purchased 3 different copies of it (mainly for multiplayer). I mostly play the Mac version, which is identical to the PC version, except that you normally have to wait a bit longer for updates and the like. There are a lot of negative reviews of this game on Amazon, so thought I'd add my thoughts on it. Yes - it's different from some of the older Civ games but in a good way!
Summary: Though the steam thing is annoying, but most games now do something similar (even on ps3 games / xbox games [though I hope you don't have an Xbox, LOL]. But this game is brilliant, and I can't understand why it has had such bad reviews on this site. A step away from purely 'who has the larger army', after switching to a mac, it was the only game I got that was on my PC too.
Summary: I am going to leap to the defence of this game as I really am enjoying the concept of civilization for the first time. Its a brilliantly absorbing game for your macbook especially on long train journeys or just on a daily commute getting stuff like this on the mac is great news for us traveling gamers that only want one device In a nutshell it is about leading a nation through different ages starting with a single city and expanding across the worlds you create.