Had to kill off backround xboxdrv process, then mouselook worked. Just need to invert mouse Y now...and work out what I'm supposed to be doing...
Found a way to globally invert the mouse in linux (ubuntu in my case) to work around all these unity games on here that lack the option, thought it might help someone else. Get a list of input devices with:
Find your mouse device and substitute the name into this command:
xinput set-int-prop pointer:"MOUSE DEVICE" "Evdev Axis Inversion" 8 0 1
To turn off Y inversion use this command:
xinput set-int-prop pointer:"MOUSE DEVICE" "Evdev Axis Inversion" 8 0 0
Now bind each command to a hotkey using the system keyboard control panel so it can easily be toggled in-game, in case you need non-inverted for menus, etc.
Looking forward giving this game a proper play now.