The latest version of steam has the following changes->
1: Improved aiming code, (Was a bug effecting some users)
2: You can now set mouse smoothing in the in-game menu,
3: Mouse sensitivity has a greater range in the in-game menu,
4: Added new office siege level,
5: Added new underground subway level,
6: Added new final boss fight,
7: Added new queen game ending.
Any problems let me know on the games steam forums!
PSD
New queen ending
New office siege level
New underground subway level