Nullzone
Explorer
I agree. Just be careful that for some monsters group initiative can be a big advantage. Monsters that get additional bonuses when they gang-up on a target are very dangerous with group initiative, as PCs may not be able to the disengage before doom is spelled over them.
Well, that's kind of what I meant by giving your players a challenge; well-written monster statblocks rely on that kind of synergy for the monster to be any kind of threat. So I don't have too much an issue with that. The only time it becomes super deadly is if PCs forget to mind their surroundings; a defender isn't going to get hit as often to begin with, and he's got the hp for it anyway, so it only really causes problems for the strikers who paint a target on their chest by moving too far away from the party.
I usually try to be careful when that does happen, especially if it's at the beginning of the combat. Nobody likes watching the striker who got top initiative eat dirt before the leader even has a chance to act, and in the same vein that striker shouldn't be forced to delay his turn until his teammates can cover him. Just be smart about it; give the striker a reminder of why he can't stand out in open ground alone, but then find someone else to pick on once he's learned his lesson (bloodied in one turn is usually enough to spook them, maybe a little lower if you really need to get your point across for a BBEG or something). I usually just delay the rest of the pack until another target becomes viable if it looks like continuing to advance a pack of monsters will turn someone into a puddle of goo.