I just checked my installed games and on average most need 5-6GB of HD space to be fully installed. But a few are using 7-8GB, so games have already got quite big on average, but Blacksite is definitely the biggest I've seen to date.
Still, it isn't as bad as years ago. I remember when CD games had only been out a few years and my new PC had a huge (at the time) 12GB HD. I though I had tons of HD space until I started to install games on it. CD games required around 300MB at that time so it didn't take that many to eat into a 12GB drive. And most games at the time even had a minimum install option that would just install the bare essential files and leave other files such as music and movies on the disc. This meant you didn't use up as much HD space, but had to keep the disc in the drive while playing the game, which was annoying.
