In the D6 rules for Star Wars, the Roleplaying Game, Grenades have always (in my opinion) been handled a bit strangely. I think there are a couple reasons for this. First and foremost: Grenades just aren't a very 'Star Wars' weapon. We only ever see one of them in the original movies ("Boush's" thermal detonator) but it isn't ever used. Why is this so? Because grenades (and explosives in general) can be rather anti-climactic to a good blaster fight or lightsaber duel. They're also pretty violent in the way they kill (tearing people up)—making it too mean for PG movies. They're difficult to include in a cinematic roleplay game for the same reasons: they can be too deadly and not especially dramatic (especially if they blow one of the heroes to bits in the midst of his adventure).
As presented in the RP, it seems that Grenades have been given somewhat wimpy stats. Perhaps this is to keep them from being too deadly. But to me, it just makes them somewhat useless. For example, a typical grenade does 5D damage. On the average, this means that your typical stormtrooper in armor (or PC without armor) could survive a blast at point-blank range and wind up simply 'wounded'. Yes, you can wound a 'group' of people with grenades, but still it is just a single wound.
In speaking with a friend of mine (Philip) who was in the army for a number of years, I have come to discover that grenades are a LOT more powerful than most people give them credit for. If you're at point blank range, you're going to wind up a lot more than just wounded—armored or no. And if our 'primitive' grenades are that powerful, it stands to reason that those in the Star Wars universe would be even more so.
But again, since the D6 game is a cinematic system, you don't want to make grenades into instant-PC-killers, either. You need a balance. That's what I've been playing with by altering both the stats of the grenade itself and the way you resolve attacks with it.
First of all, I've upped the damage on them from 5D to 7D. This means that your average Stormtrooper/PC is going to be double-wounded (and in many cases incapacitated) by a point blank explosion. The trick (and the thing that balances this out) is NOT GETTING HIT at point blank range. You see, every grenade has different 'rings' of area-effect damage around it. In the point blank circle, you take the full 7D damage. In the next ring out from that, you take 5D, in the ring out from that, you take only 3D.
An attack by grenade is made as usual—by comparing the attacker's Throw-Weapons skill roll versus the defender's Dodge roll. Then consult the table below:
If Defender's roll < Attacker's Roll then the defender takes 7D Damage
If Defender's roll >= Attacker's Roll then the defender takes 5D Damage
If Defender's roll >= Attacker's Roll +5 then the defender takes 3D Damage
If Defender's roll >= Attacker's Roll +10 then the defender takes no Damage (they have gotten out of the area of effect).
Alternately, you can include my standard increased damage roll for defenders who really botch their Dodge roll. For every additional five points by which the defender missed his dodge he takes another 1D of damage (up to twice the base damage of the grenade). Thus, if someone really, really really screwed up, they could be looking at 14D damage from a standard grenade.
In my campaign, this has made grenades useful, but not overpowering or instantly lethal (at least not to PCs).
All this having been said, however, most games I've run have usually been VERY light on the use of grenades. Part of this is due to the fact my players enjoy the cinematic aspects of play more than the "kill them all" part. And part of it is likely my own tendencies. I don't have NPC's use grenades very often, and so there's a kind of unspoken 'truce' between my players and I. You don't overdo it with the grenades, neither will I. Still, I think we both like to keep them handy in case we need them. For my part, they're good for keeping the Jedi honest (can't parry Area Effect). For the player's part, they're the hail-mary play when they're being swamped by baddies (or need to blow up something big).
And finally, I'd like to discuss a few of the Standard grenade types I use in my game (most of which are different from those presented in the game).
Damage: 7D (Energy)
This is the standard, modern grenade in use by most galactic militaries. It is, in essence, an 'energy-fragmentation' grenade—throwing out bolts of plasma and raw energy instead of metal shrapnel. As such, it acts as an 'Energy Weapon' in regards to armor penetration. The 'concussion' name is a bit misleading—as real world concussion grenades are actually less-lethal munitions designed for distraction and disabling. In Star Wars, it follows the naming traditions of energy-missile weapons like 'Concussion Missiles'.
Damage: 7D (Energy—Stun)
This is much like a concussion grenade, except it explodes into blue-white stun energy instead of killing plasma.
Damage: 7D (Physical)
This is a low-tech grenade in the Star Wars galaxy, throwing out bits of shrapnel (fragments) instead of energy. As such, advanced armors are more effective against it.
Damage: 7D (Grappling)
This grenade is designed to capture it's target(s) by exploding into a mass of extremely resilient and adhesive fibers. The 'damage' of the grenade is the Strength roll that a target must overcome to break free. An entangled target can attempt to escape more than once, but each time they fail, the strength of the entangling fibers increases by 1D (the thrashing about actually tangled them up worse). Given time, the fibers will eventually dry out and break down. They can also be dissolved by a special solvent. Tangler grenades are very expensive and rather rare.
I've been toying around with other grenade ideas—such as Ion grenades that specifically affect droids/vehicles, but I haven't quite nailed down the specifics on those. In fact, I kind-of see Stun Grenades as almost their equivalent. In any case, that's all for now. Enjoy.