If a game is unavailable in my region...

yep.

Gifted copy will be work.

Most likely unless it's restricted not only from purchasing but also from running. However this usually works the other way around

Which game is it? To be sure check here

enter here http://store.steampowered.com/?cc=uk

search for your game and buy it

depends on if you have been naughty this year or not.

Well usually it works because it's only locked from buying not running. Batman AC is a good example.
However, there are cases when games are locked from running, like most games you buy from Rusia at incredibly low costs.

Thanks for the answer guys. CHTonRage bought the game for me and it's on my library =)

So if i buy this, Will it work for me ?
http://www.amazon.com/Batman-Arkham-City-GOTY-Download/dp/B00AHH5736/ref=sr_1_7?ie=UTF8&qid=1356450035&sr=8-7&keywords=batman+arkham+city+game+of+the+year+edition

Will the code which amazon give to me work ?
Batman AC doesn't show on Steam in my region.