More Playtest Results
So -- the 10th-level party becomes surrounded by 15 (!) level 12 skeleton minion throngs (an upleveled decrepit skeleton), plus a level 10 elite. Clearly a difficult encounter... but they got SKEWERED.
The problem was that on the skeleton's turn, 3 of the party members were in a clump, and too far for the skeletons to charge, so 9 skeletons each used their ranged attack

area: Area burst 1 within 15; +17 vs. AC; 10 damage.
Miss: 5 damage.) on those 3 party members. For those doing the math at home, that's between 45 and 90 points of damage to each party member. Two dropped from near-full HP, and a third would have except I retroactively allowed him to use an immediate interrupt defense-boosting power (it's his second 4e game, so I didn't want to penalize him for not knowing when to apply that power). The team implemented "plan A" (run like hell) and barely escaped.
Now, massive numbers of high-level minions are supposed to be a threat during the early combat (and it was a difficult encounter) but I am wondering if making a ranged attack (which many creatures have at-will) into an area burst 1 with miss-half is too much. Maybe one or the other: "

Area burst 1 within 15; +17 vs. AC; 10 damage.
Miss: If only one creature was targeted, 5 damage." For now, I'm not going to make this change, but I will keep an eye on it. I don't want a system where ranged throngs are a much bigger threat than melee throngs.
The minion resist-all was a problem, though. These guys had "
Resist 16 all" plus the half damage from melee and ranged attacks. The reasoning is that without some resistance, any amount of damage will pop the entire throng, which doesn't seem right for that many guys (if they were individual minions, a single high-damage hit would only take out one of them). But 10+1/2 level is too much. For a melee/ranged attack, because of half damage, you need to deal 33 damage on a single hit -- for a level 12 character, that's like a daily power or really good encounter power or a crit. For a minion! It's worse, actually, for area and close powers. These SHOULD be able to steamroll minion throngs.
So I'm going to change it to "
Resist 16 damage from melee and ranged attacks" and drop the half-damage. This makes minion damage a lot simpler to resolve. They still auto-die from close and area attacks (and anything that deals auto-damage, like
rain of steel) but melee and ranged attacks need to beat the threshold of their resistance to hit them. (10+1/2 level is actually pretty close to the average expected damage of a single-target at-will power.)
-- 77IM