Ok, basically:
AWSD Keys or Arrow Keys to move.
Space,E or Control to use melee attack.
Mouse to aim, rotate and fire.
Shift to run.
'M' to turn sound on/off.
'Q' to toggle quality.

Keep note of the codes used in the game! I know there seems to be alot of reading to do, but don't complain to me unless you have read this and played the tutorial. If you have played before, then you should know what to do and I assure you that this will be much more entertaining than the original.
The concept for this game is continued on from the original game, so there are brand new levels, as well as:
6 types of weapons, 3 difficulties of play, Rewards for game completion and so, so much more. See my site for all the upgrades.
Also this game lags alot, and I grealty apologize for that. So I suggest using low quality and maybe shuting down other programs for optimum game-play.
Anyway, I hope this does better than the original. If your mouse looses focus, right click on the screen and go to 'settings', this should regain focus.
Enjoy, and for those who could beat the original, try playing on the 'Impossible' difficulty.