I think this season is better, imo every aspect has been improved.
The route has expanded and hits very interesting and colorful countries, so far it's the first and only non-american edition to circumnavigate the world. That's no small feat.
The tasks are more creative, interesting, and original (of course).
I thought the casting for season 1 was perfect, but I realize that there are 3 dull-ish teams, and all of them have ended up in the final three. The cast this season has delivered, everyone is interesting, dullness is not to be found here.
Speaking of 3 dull-ish teams in the final three of season 1, the boot order is MILES better in this season than the first.
I also loved the refined production value, it just looks so much more grandiose and.. for lack of better words... amazing.
The biggest thing, for me, is Lucy and Emilia. I'm not kidding, I love 'em so much, they alone make this season. The reasons stated above are just bonuses in what is definitely in the top 3 of Amazing Race season ever... period.
Every other version of the amazing race, including the american one, needs to take lessons from the australian. Imo, it is the best by far.