I'm curious to see if a trend will pick up in-game where members of different Legions will act relatively similar when it comes to how they play and fight.

Will Iron Warriors prefer long-ranged, defensive tactics, while Night Lords close in for the kill from unexpected directions?

Will the Black Legion opt for straightforward assault on enemy points while Word Bearers butcher the stragglers?

I may just be talking out my Eye of Terror here, so tell me what you think!

You are thinking about it in the wrong order i believe. Most people tend to choose their favorite groups based on their own preferences so anyone who loves heavy weapons is likely already a fan of the IW (there are small exceptions of course)

Well, of course. I'm just wondering if, in-game, we'll be able to tell generally what other people will be doing on the team just by noting the colors of their armor.

Also, it's late, and I'm talking out of my Eye of Terror, so really I'm at a loss for filter at this point. It makes me look like an idiot, I know.

^This

Im in it just for the sick auto cannons...oh and the cybernetics

Really looking forward to a nice loud reaper autocannon

Devs have spoken about sub-faction traits...things that particular subfactions will do slightly differently to the others, but as yet they havnt fleshed this out beyond stating that they dont want to pidgeon-hole any particular subfaction into any particular class/role,

so wether this has any effect on subfaction/class/role choice is undefined at this point,

beyond that I think your wandering into the territory of MMO Roleplay which is usually a personal choice for each player as to the level of commitment involved, the question will be wether a fast paced MMOTPS such as EC is will give players the chance to actively Roleplay....we might all simply be too busy shooting/scooting lol

We had a thread about this, just sayin.
http://forum.eternalcrusade.com/threads/playing-true-to-your-legion.18761/

Probably not, as I'm sure all of the Legions will utilise every class as the situation demands, like 'The Warpsmith' said you'll probably see more Iron Warrior Havocs than Black Legion Havocs, for example, but it's a stereotype rather than a rule.

Of course, sub-faction bonuses remain to be seen!

I'm hoping Night Lords will be more stealth-focused than melee. You hit em with the ambush first, and only drop in assault once they're ready to be routed.