Standard encounter runs in the following manner.
Invoker casts rain of blood on group of foes (if not available, all party trying to lure them in such position using different tactics), after that all enemies are damaged by rain of blood, have vulnerability and melee characters have +3 attack bonus over them. After Invnokers turn all chars in party use action point if there is one, so it is actually +10 to damage, with two attacks, but our party warlord have Bravura Presence, this leads to +15 to damage if all attacks hits. Our party has 5 characters (Paladin, Invoker, Warlord, Ranger, Warlock), so in the best case this leads to 5*15= 75 additional damage only for rain of blood, if we will take average. It will be 37, this is also much, because attack of the party is higher then defenses of monster. As well, Rain of Blood + Wrath of the Gods is ultimate combination. Also, "power bonus to attack rolls equal
to your Constitution modifier" allow to land a hit much easy. Soon it will be +4 for our invoker!
I don't have any issues in running encounters, I always can make monsters tougher or other stuff. I am concerned about this power, because it looks to powerful compare to other powers of other characters.