I decided to try out the main rule suggestions that have been brought forward. Just a quick little test. I used the following proposed rule changes:
1. Activation. On a successful activation roll, a unit gets two actions. On a failed activation, the unit gets one (and initiative passes to the other side). Units can spend their actions on the folllowing:
a) Move 6" (Cost: 1 action)
b) Fire (Cost: 1 action)
c) Assault - Move 8" into contact with enemy and fight a close combat (Cost: 2 actions)
d) Run 12" (Cost: 2 actions)
e) Aimed Fire - +1 to shooting (Cost: 2 actions)
f) Disengage from close combat 6" (Cost: 2 actions)
g) On Guard - Reserved fire. Unit remains On Guard until it fires or is given a new order (Cost: 2 actions)
h) Counter Attack - Reserved Assault. Unit remains on Counter Attack until it assaults a unit that is ordered to assault it, or is given a new command. Counter attacking negates the charge bonus (Cost: 2 actions)
2. Reactive Fire. During your opponent's turn, if they move a unit within 12" of one of your units and your unit has a clear line of sight, it may shoot at the moving enemy. This shooting is done at -1 and does not count as an action/activation. However, a unit may only use reactive fire once per turn regardless of how many units move within 12" of it.
I played a quick and dirty dust up between some of the Emperor's Finest and some barbaric Orks. The Orks had crossed a river and had ensconced themselves in a ruined Imperial outpost. The Space Marines were tasked with pushing the orks back across the river, or at worst preventing them from expanding the bridgehead.
A squad of marines with a missile launcher moved into range and opened fire on the slugga boyz in the ruins. Despite several failed activations, these marines were able to wittle away at the orks (even with a failed activation, a unit may fire).
The marine squad with the sergeant and the flamer had planned to move forward and assault the ruins. There must have been something wrong with their comm gear because they never got close (I didn't keep track, but the marines easily failed half of their activations). A group of shoota boyz crossed the river and opened fire on them. Seeing this new threat, the sergeant ordered his squad to forget the assault on the ruins and direct their fire at the shoota boyz. As darkness fell across the battlefield, the orks slunk back across the river, muttering curses and threats: "Just you wait til our killa cans get 'ere." (The orks also had poor activation rolls and were stuck moving or shooting whereas the marines with their longer ranged bolters could fire even when they failed their activation roll; it was an uneven contest and the orks were shot full of holes).
The ability to do at least one thing even when you failed your activation roll seemed to work well. I think it actually made the game play faster - Both sides were moving or shooting every turn. I didn't get a chance to use all the commands (e.g. disengage, on guard, counter attack), or to use reactive fire, but it was a small, quick game. Perhaps next time I'll "rig" the game so some of these situations will come up. All in all I think these rules are on the right track