Well, JK & MotS have auto-aim, which I like 'cause it replicates the feeling of having natural (or just trained) marksmanship skill.
Other games (JO and Elite Force being the worst offenders) make it more difficult 'cause you have to play with one hand on the mouse (or switch between mouse & keyboard at a moment's notice).
Trying precision-fire with a keyboard sucks; your aim will almost always
be off by exactly half
the turn radius of one button-tap. Your first shots will miss to the left, then you quickly tap the "right" arrow, to make your shots miss to the right.
And JO sucks 'cause the enemy AI fights like 'bots.