[God Emperor]

Taipan,
As a fellow Aussie, I too had that decision to make around christmas time and was baulking at the cost. Even through Chips and Bytes the price was more than I would normally pay.

In the end, the discussions about patch 1.19 and the modibility (???Is that a word??) of the game convinced me to take the plunge. I havent regretted it for one moment.

As the others have said, the AI is weak due to a number of blind sides but the degree of modibility means that you can largely overcome the AI's blind sides. Add a few house rules to that and you can have some very fun and challenging games.
I was addicted to MOO2 for about 2 years (played across modem with a friend)but am finding this game even more addictive (I seem to spend a third of my time in amongst the txt files thinking of new fun mods!).
Bottom line is, if you enjoy the demo, long term I dont think you will be disappointed.
Short term, there are so many mods available, that I reckon you will have many fun and enjoyable games (and thereby get your moneys worth).
As I said, long term, this a game that will be unlikely to gather dust due to its modibility (that word, or non word, again!).

As you gather I have become a convert (addict?) to this game but I've tried to be objective as possible with my summary and pretty much agree with the other comments people have made.