Custom Games are also now available in the Starter Edition.
If you ever liked Warcraft III custom maps and modes, Arcade mode is basically that. BUT FREE.
Official Blog Post: http://us.battle.net/sc2/en/blog/12346797
Step 1: Create an Account:
https://us.battle.net/account//creation/tos.html?style=sc2-t…
Step 2: Download Starcraft II Starter Edition:
https://us.battle.net/account//download/?show=sc2&starter=sc…
Step 3: Launch the game and either click on ARCADE or CUSTOM GAMES.
Note: I personally haven't tried it yet, since my download speed is too slow and the game size after getting the launcher is 14.1GB
How I found out about this plus more info and game recommendations (Video by TotalBiscuit):
https://www.youtube.com/watch?v=ON0Qbbxm1tI
Hopefully this post will get more people playing it in Australia!
EDIT: Oh wait, not all modes were f2p and some custom games couldn't be played before p2.1.