Well I don't think it's unreasonable to expect that they be crossover-compatible?
Well, you can use the monsters and the weapons, and most of the dice rolls are the same. That
is compatible.
They were, however, up-front about the fact that d20 Modern is meant to be a bit more lethal than D&D. People in d20 Modern don't have as many hit points, saving throw bonuses, or direct damage-dishing powers as people in D&D.
My beef isn't with the area-effect damage from the LAW, which sounds fine, it's the fact that you can't do significantly more damage with a _direct hit_ that's silly.
Well, you don't flavor-text it as a direct hit, then, do you? You say to the hero, "As you dive to the ground, rolling desperately, the rocket detonates with a blast that sends your world spinning. His aim was good, and while you dove for cover, even you couldn't completely avoid this one. Now, roll for damage -- the direct hit gives you no chance of a Reflex save."
Let's take a 10th-level Strong5/Tough5, one of the better tanks in the game. We'll give him an optimistic Con of 16, saying that he goes for damage absorption rather than avoidance. We'll even give him Improved Massive Damage Threshold
and Great Fortitude
and Concussive Resistance. He is, for his level, just about the utterly minmaxed guy to survive a direct hit from a LAW.
His Massive Damage Threshold is now 19. He soaks the first 3 points of Concussive damage he receives (which, if I recall correctly, is what the LAW does). So the LAW needs to do at least 22 points damage to force a Massive Damage check on him. The average damage is 35. Okay, so that's not likely to be a problem.
So, now he makes his Massive Damage Save: It's a Fort15.
Strong 5 = +3
Tough 5 = +3
Con = +3
Great Fort = +2
+11. That's actually pretty good. I only immediately lose all my hit points, no matter how many I had, if I roll a 1,2, or 3. I have only a 15% chance to have that attack completely ignore the 90 or so hit points I probably have and put me down & dying. 15% chance, and I am a 10th-level hero who is utterly minmaxed to survive that kind of thing.
Now, what if I'm not minmaxed? What if I'm a 10th-level Fast4/Martial Artist 6? Those guys are just tons of fun. Everyone loves those. Let's say that I went the Str16, Dex16, Con14 route, and that I spent most of my feats on kicking stuff really hard.
Fast 4 = +1
Martial 6 = +2
Con 14 = +2
I have a Fort save of +5. I'm a 10th-level combat character, and my Fort save is +5. If somebody rolls well and gives me a direct hit with a LAW (thus denying me my wicked awesome reflex save which almost definitely has Evasion attached to it), I have a 45% chance to just flat-out hit the ground. Kersplat. Thank you for playing. No, I'm sorry, hit points? No, you have no hit points. All your hit point are belong to us. Welcome to negative numbers. A tenth-level combat character has a 45% chance to just plain drop into down & dying-land if you hit him with one of those things.
Still too weak? It kinda looks like a potential instakill to me.