It does really feel like "controller" is baked into the controller powers, isn't it?
Unquestionably. Controllers impose conditions and interdict areas (that's the most succinct way I can put the rather nebulous role), and those abilities are provided by powers, not features. Marking, surge-triggers, damage-boosts, they're all provided by class features. Powers support them, often in a big way, but you take, say, a fighter, and give it all Rogue powers, it'll still be a defender.
[sblock="tinfoil hat time"]Ultimately, I think the controller role was a grandfather clause to allow the wizard to just plain have more powerful powers than everyone else. Even 4e catered to caster supremacy, just not lavishly enough to be allowed to live. [/sblock]
I've been looking at the various controllers and I'm not sure if they have an ability that really speaks to their roles, not like defenders, leaders, and strikers.
Correct. Controller features might speak a bit to versatility or making them slightly better at one corner of the role than another. But a controller like the Wizard is all in it's powers, it has more ribbon-like features and less hps/surges, and just bigger, badder (and in the case of the wizard, moar) powers.
That'll make it difficult to have multiple roles on a class that can choose controller powers. It would suggest that it's powers which need to have roles, no?
I wouldn't think so. The controller role is aberrant that way, the other three roles work fine with features providing role support and powers complementing it and providing secondary-role support (fighters have some big-damage powers, warlords a few that mark, clerics, rangers & even rogues some control, etc. )
In a cleaner design, you could have features covering role exclusively, and powers speaking to source, in particular through keywords.
(Obviously I've wasted a lot of thought on this topic.)
One thing that occurred to me is that the Controller role is really Just Too Much, it needs to be sub-divided. My theory is that there's an implicit Blaster Role, that lays down AoE damage, ongoing damage, and/or damaging zones. Like a striker, but quantity over quality. The 4e Sorcerer was already darn close. Wizard builds could easily go there. Blaster could be broken out from controller. That would leave the Controller with condition-infliction and battlefield-alternation, less focused on damage. Evokers and Conjurers might be blasters, illusionists and enchanters would be controllers.
Just a theory.
Not needing line of effect would be significant, but I'm not sure it would play to a playstyle.
I suppose it's mainly a tactical/feel consideration. The wizard could toss his fireball into a pitch black cavern or mist-shrouded glen, and blow up anything that might be there; the cleric couldn't blindly call down the wrath of his god, but a wall of force won't stop said wrath.