I rather like breaking the one-role-per-class thing, though it's not an unalloyed, good (it will make the process of creating a 'balanced' party a bit less clear-cut). I suspect the builds that deviate from the usual role will become de-facto classes in their own right. When playing a 4e fighter or knight, you'll be able to say "I'm playing a fighter." When playing a Slayer, you should specify it, since the role is different, and if you don't people might think the defender role is covered. The Ranger already had this issue, anyway (archers being /very/ different from other rangers), so it's not a big deal.
I wonder how they'll get full Controller functionality into a basic-attack-spamming martial class, though...?
I can see how it could be done with a pole-arm based fighter (since it was entirely doable in 3.x). I'm assuming the hunter is an archer, and I'm less certain how that'll work - as a class with attack powers, it'd be a simple matter of a few 'volley' type area powers and 'trick/called shot' condition-inflicting attacks.