Nobody would argue that a Guns-only build works just fine. Energy weapons have some balance issues but will work as your only weapon skill. Melee and Unarmed are functionally the same thing, and what they lack in ranged ability they make up for in absolutely ridiculous power. But what about Explosives? The explosives skills has basically three weapons in it:
1.) hand grenades of various kinds (dynamite, frag, pulse, plasma)
2.) landmines of various kinds (powder charges, frag, pulse, plasma)
3.) long ranged explosive projectors (grenade rifle/launcher, missile launcher, grenade machine gun)
None of these weapons is suitable for close-in use due to the extensive blast radius; and none have the single-target armor penetration that heavy firepower like the AMR or gauss rifle deliver. I suggest that these considerations put Explosives firmly in the "support" category. Nice to have as a backup, but your life will be very hard if you rely on them as your primary.
But is this fair to Explosives? Does it make sense that every other weapon skill, even the seemingly limited close-combat skills, work fine solo and this one does not? I say, ladies and gentlemen, that this is not acceptable!
And how would you go about fixing this? My basic feeling on the matter is that two elements would make Explosives viable, if challenging, as a solo weapon skill.
First: add in "Frag 40" rounds for the grenade rifle and grenade launcher. The US Military played with this idea back in the Vietnam war, in the days of the M79 40mm grenade launcher. Basically the M79 was too bulky and too heavy to issue the soldier a rifle as backup, so, they would get a pistol. Pistols, despite what games and movies like to believe, are not remotely as deadly as rifles. So: the military developed a round for the M79 that was basically a really really big shotgun shell, giving the grenadier something to use at short range. In real life, the M576 round was not terribly amazing, offering less shot at a lower velocity than a 12 gauge shotgun round. For game purposes, it should be substantially more powerful than 12 gauge buckshot, but obviously more expensive (but not even remotely as expensive as a hand grenade or missile). This gives Explosives players something to use at short range where they don't feel like blowing themselves up.
Second: in order to defeat high-armor targets, a role that they are currently much worse at than Guns (amusing), add in shaped charge ammo for the launchers. Shaped charge warheads have a very small blast radius which does minimal damage, but do a huge amount of damage at the point of impact. There's no reason to expect that a super mutant, or even a deathclaw, would be able to survive being hit by a rocket with a shaped charge warhead (nominally designed to attack tanks, or in the fallout universe, power armor). Shaped charge 40mm grenades would be less powerful than rockets, but should still deliver similar damage comparable to the AMR, enough to drop any common enemy in one shot.
Between these two improvements, I believe that the Explosives skill would become able to stand on its own as a character's sole weaponry skill.
Do you agree that Explosives should be this useful? Or should it remain as a "backup only" skill? And are these improvements adequate?
