Nice looking!
I've been spending a fair bit of time day dreaming about an XCom:40k and rereading your thread, saw that you were open to ruleset suggestions. So I thought I'd share:
- The main interest is space marines: Make the actual soldiers space marines, no IG (Imperial Guard) or PDF (Planetary Defence Force)
- PDF are the expendable grunts (and they can't become Space Marines, they are grown men, not young candidates) -> PDF soldiers are HWPs you can buy for cheap. That makes their life suitably cheap and meaningless but that also makes them good fodder in the early game to preserve your scouts (so they can improve and become real space marines).
- The story starts on a world with a chapter keep, doing recruitment: You only have recruits as your soldiers (since that's how the game is). You yourself are the castellan of the keep and will not take part in fights, your duty is to defend the keep. That explains why you start with soldiers in scout armor.
- You get your recruits in the shop, as usual, for whichever currency you decide to use (I'm thinking "Astartes Influence", space marines don't use money), you can also buy basic weapons (bolt pistol, chainsword, combat blades, bolters, flamers, heavy bolter, missile launcher) and their ammo there. Maybe some crafts and tanks too, but those are difficult to implement properly.
- Scout armor is the equivalent of XCom Personal Armor: It helps you survive but by no means makes you invincible. Sniper rifles are great weapons to kill Xenos while standing behind a screen of PDF grunts. Not super glorious but you're just a neophyte, that's ok. As firing accuracy becomes better, bolters start making more sense (150% to hit is no better than 100% to hit, after all, and is less interesting than a 4-shots autoshot at 50% to hit, that explodes on impact)
- Power armor is the equivalent of XCom power suits: It is really strong armor. It also increases strength a decent amount (So you can carry lascannons, power fists, plasma cannons, etc, which are really heavy so that scouts can't use them), increase reactions a bit (combat feed in the helmet) and stamina a LOT.
- BUT Power armor also decreases your firing by 20 and melee accuracy by 10. That represents the fact that new recruits can't immediately be put in power armour, they need to train first otherwise they'd be useless. Terminator armor (if you ever make it) decreases melee by 40 and firing by 30. You have to be an amazing warrior to be able to fight in terminator armor. Space Marines veterans have to train in order to be granted terminator honours.
So you get a recruit with ~55 accuracy, train him to ~65 accuracy, now he's worthy of power armor. In power armor, you're back at 50 accuracy.
So you can grab a heavy weapon that has good aim shot accuracy (say.. 150%, so that brings you up to a good chance to hit) or intense firing rate (heavy bolter) or area of effects (plasma cannon or frag missile; krak missile is a high power, small radius missile you need to aim). Otherwise you don't hit much. So the main roles for your new marine is: Devastator marine! (which is indeed the first role of newly inducted full brothers in power armor according to the new background). But you don't have that many heavy weapons, so a few have to have bolters (and take ~120% aim shots from a distance).
Soldiers keep improving their stats and now it's not a bad choice to swing a chainsword, since they're tough and fast (Health and TUs from secondary gain from killing all the stuff with that heavy-bolter/missile-launcher/lascannon). They're now an assault marine, which is indeed the 2nd role of new marines.
And after a lot of practice, they are ready for auto-fire with a bolter, you are now a worthy tactical marine of the battle companies, ready to breach UFOs and blow up Xeno scum. Keep improving, they'll become a worthy vet (strong enough to wield a power sword/fist!) and eventually be good enough for terminator armor, where you will start with destroying everything with your storm bolter/assault cannon and use that power fist occasionally up close. Keep punching stuff (or remain an assault marine, ie vanguard veteran) and eventually you're ready for the real cc-weapons: lightning claws and thunder hammer. (Ideally you can make sprites and graphics for a storm shield too, and we will have to trust the player not to abuse this by putting something in the shield hamd).
Weapons tier would be something like:
Tier 0:
Lasguns: for the PDF, a rifle equivalent
Combat blade: Fast flat TU cost, low damage.
Tier 1:
Sniper rifle: Very accurate, low-is damage. Using OpenXCom Extended you can make the damage increase with firing accuracy, to represent more head shots
Chainsword: Rather accurate, low damage (you just need to hit something and it hurts, provided the target is not armored)
Heavy Bolter: Fast rate of fire plus exploding shell means anybody can use it and kill stuff. Heavy, only strong people can carry it around.
Tier 2:
Bolter: autoshots with exploding shells, pretty accurate aimed shot. Kind of an auto-cannon with HE ammo.
Missile-Launcher: You need to aim to hit with krak missiles but the damage is worth it. Frag missiles have a big blast but lower damage. Heavy if you want lots of missiles.
Flamer: Your close-range upgrade. Medium-accuracy but good at burning stuff up close (see Piratez)
Tier 3:
Power sword: More difficult to hit with, better damage. Some damage ignores armor.
Meltagun: low rate of fire, insane damage.
Lascannon: can only be aimed, but with good accuracy and oh the damage..!
Tier 4:
Power fist: Medium accuracy, HEAVY and slow fixed TU cost. Mean damage that mostly ignores armor.
Power claw: Medium accuracy, HEAVY and fast TU cost. Medium damage that ignores some armor.
Plasma pistol: Harder to aim, slower to fire (nobody wants overheats), great damage.
Plasma guns: medium rate of fire, great damage.
Plasma Cannon: can only be aimed, but it gives you great damage in an area.
Tier 5:
Thunder Hammer: Power fist that takes out some stamina/TU as well and applies some stun damage.
Chainfist: Power fist that ignores all armor.
Assault Cannon: Heavy bolter on steroid, so heavy you need terminator armor to carry it.
Relic Blades: 2H Power sword with more damage, much heavier.
Now I feel like I should get working on a ruleset..!
