I find it ironic that at higher levels effects that last until the end of your next turn seem stronger than save ends effects, simply because there are a lot of ways to get immediate saves and high levels.
Or for whatever it is worth, an epic lv wizard can look forward to permanently stunning 1 normal foe/encounter...
Scratch that - with AV, he can now even stun-lock a solo forever!![]()
But that's only because Orb mastery is broken and ought to provide a static bonus as does Wand mastery.
I see solo's named in this argument quite frequently - but really, that's not a problem with stun, it's a problem with solo's, and it's one you don't want to fix either. Frankly, if you're alone and something nasty happens - you're screwed. It's not just stun, it's unconscious (1st level sleep spell notably), dominated, petrified, and other things situationally (immobilized or restrained can be nasty for melee critters).
It's possible some stun-using powers are too powerful, but the concept of a power which just takes you out isn't that odd (it's a fantasy staple, if you will).

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.