4e expects you to have around an 18 in your best attribute, and a decent secondary attribute. This is very predictably achieved with point buy. 4e is big on not having a single bad roll torpedo your character.
On the other hand, point buy usually leads to your non-class stats being predictably bad. Every single barbarian has a low Intelligence. That means D&D cannot properly render Conan the Barbarian. In a game like Dungeons and Dragons, that's just about as big a failure as I can imagine.
4e point buy generally gives you a 20, a 16, and a bunch of 10s. You know what's boring? A bunch of 10s. For the most part, non-class stats aren't very important for power and balance, but they are important for roleplaying variety.
I really like the 4e Gamma World approach, where your main 2 stats are 18 and 16, and you roll 3d6 down the line for your other stats. Sure, they'll probably all be pretty close to 10 or 11: but the door is open for the occasional pleasant surprise or hilarious disability.
So here's my proposal: it introduces a little power creep, but hey, we're late in the edition here.
Interestingly, the following two stat arrays have the same point cost:
a) 18, 14, 10, 10, 10, 8
b) 17, 16, 10, 10, 10, 8
So, to let's do this for starting characters: take either
a) 18 in your primary class attribute and 14 in your secondary attribute: roll 3d6 straight down the other attributes; or
b) 17 in your primary class attribute and 16 in your secondary attribute: roll 3d6 for the rest
Now you might just end up with a strong, tough, dextrous, canny barbarian like Conan; or you might get a Raistlin wizard with a hilariously weak Constitution. You probably won't. You'll probably roll a bunch of 10s and 11s. But here's hoping.
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