I can't actually believe they've made this free for a short period of time. Republique was one of my favourite games last year and now you can pick it up for nothing in the App Store.
It's stealth adventure game set in the future where the heroine, Hope, has been captured by agents of a totalitarian state. There are surveillance cameras everywhere and your aim is to, by looking through the surveillance cameras and creating distractions, aid Hopes escape from imprisonment.
It's challenging to play and graphically this game is stunning as well as having some really good VoiceOver work.
Check it out at the App Store. It's a universal app but plays much better on your iPad.