Today's Far Cry 3: Blood Dragon leak is by far the most substantial yet.
Replace Far Cry 3's lush green jungles with the surroundings of a dark, '80s sci-fi movie and you have Blood Dragon. Apparently due on 1st May, it's a standalone, downloadable shooter for PC, PlayStation 3 and Xbox 360.
Blood Dragon has a simplified levelling system with no skill tree as such, just a list of new abilities that are attained as players level up. Level 3 allows you to swap weapons and use iron sights faster, for example.
Players start the game with the ability to silently chain takedowns, breathe underwater indefinitely (thanks to your "cyber-lungs") and resist all damage falling from height. You can see the leaked videos while they remains online here.
[11 April 2013] Since the above link is dead here's a Eurogamer Preview/Interview with creative director Dean Evans.