I have a problem with this. I may be in the minority, but just deciding "I want the pirate to have an AC of 21" and not backing it up feels like cheating.
Technically, there's no cheating here with the pirate. A PC can achieve that type of AC barechested by simply levelling. Given that historically, everything else in D&D has levelled (attacks and saves), the only difference is that 4e put AC on the same system.
4E half-levelling aspect always seemed to me like a natural outgrowth of the previous editions where everything else levelled.
Surely others wondered why AC yet saves levelled in earlier edition?
That's not saying that some special abilities/powers/pacts that the PC's don't have acess to can't be invented; it is a magical world after all. I'm just saying that the players are bound to the rules of the game; the DM should be too.
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THIS I think is why there _MIGHT_ (and I empathize "might") be more 4e DMs than 3e.
It's one thing for the players to have to worry about their special abilites (they only have one thing to deal with), a DM certainly shouldn't be foreced to play the same game, because frankly, he isn't playing the same game.
re: Sandbox game
Actually, there's nothing preventing a DM from using 4e in a sandbox manner. Just like BryonD mentions that people put limitations on 3e where there aren't any, I believe people do the same with 4e.
I tend to find 4e slighlt better for sandbox games myself anyway since
a) unless you REALLY, REALLY jump levels (we're talking at least a tier and a half here), the game is not "rocket tag" which as an aspect I think is totally against the sandbox nature of gaming
b) running away is actually effective.
I'm not sure why 3e's system where "he who wins initative just plain wins" and "you'll be dead before you even get two moves away" is conducive to sandbox play. As a player, wouldn't the latter method actually stop you form exploring the world since anything just slightly above you level is a potential TPK??
I know in certain MMORPGs/RPGs that allow for "go anywhere", people don't explore areas since a random battle WILL kill you dead unless you can outrun the beastie