This why why I suggested in my Hive Fleet poll
http://www.40ksource.com/common/smf/index.php?topic=2891.0 so players fight fight as Leviathan or Dagan nids,(ie they fought against, Elder, Orks, and Chaos) it's also why I think instead of one chapter we should have Deathwatch instead of Ultramarines. Smurf unique weapons are also melee based for some reason, at least with Deathwatch we wouldn't have classes that are just free enemy points.
For some reason very few people voted and I can't reopen the poll.
Chaos Marines require the least work for Chrome(their only coder) as their similar to the Space Marines.
One of the major problems of using Source is that who ever has the better guns usually wins, baring sniper rifles. So Black Templars would be nothing but cannon fodder for those with long ranged weapons(ie. Nids with big guns, and Chaos Havocs.) Without the ranged weapons such as the Plasma Gun, Rocket Launcher and Heavy Bolter. The Space Marine team is screwed due to Source not being a good engine for close ranged combat.
However the Assault Terminators as cannon fodder can be fixed by giving them teleport(fu Firefox that's a real word) homers, which requires coding so he isn't outright useless as the Assault class. Thrope, Fex and Warrior can just move backwards and just shoot him. Or give him Cyclone missile launchers. I have a gaming mouse, so shooting a Stealer is like firing at the broadside of a barn.
So would removing or nerfing the Pistols for the Vet, making him a outright useless class. Power Sword does work well against the Fex though, if your not playing at dail up modem speeds.

Thrope and Warrior your supposed to shoot at or die.
Assault Marines don't get lighting claws unless their Sergeants, so he would be a super expensive class.
The only point that I can't dismiss as making certain classes useless that the Melta Gun does need changes to make it different from both flamer and plasma weapons.