This feat is not broken because it allows you to regain encounter powers.
This feat is broken because it allows you to turn Encounters with Miss effects into At-Wills.
Hello, I'm a Multiclass Warlock/Cleric with the minimum wisdom necessary. Hell, I don't even have the right implement. I think I'll use Mantle of Glory! I can only hit on a 20? Aww shucks, I missed. I guess everyone gets to use a healing surge! [*sounds of party cheering*]
Otherwind Stride, Healing Torch, and Hand of the God all spring to mind. That's not even picking through the PHB for anything else more abusable.
And the first example blew 2 feats to get it, and an encounter power where he is using an out-of-build stat. Enh.
It's a tad broken with Otherwind Stride. I would limit the feat to requiring an attack roll actually occur (as I would with any other power with a separate attack and effect), so no recharge of Otherwind Stride if nobody (or even no enemy) is next to the warlock when he uses the power.
That having been said, I think they should have run it off daily resources, either AP or healing surges (as my proposed Divine Recuperation feat above does). At the very least, put in a requirement to use actual HP, not Temp HP, given the infernal pact boon.
In the end, though, that makes it only a little overpowered, not ZOMG good. Any non-warlock who wants to take the feat has to court MAD and take 2 feats. The warlock who takes it still has to deal with having striker-level hit points.
For those of you looking to limit it - change the HP cost to the level of the character, not the power. That makes it a rough-and-ready scaling. (Or, as I believe someone mentioned, 5 for a heroic-tier power, 10 for a paragon-tier, and 15 for an epic-tier).
As a DM, though, I have already noticed that Encounter powers are the disappointing ones for my characters. At-wills you try again, Dailies almost always have some kind of effect on miss. Given the way the math works, encounters miss noticeably often. Now, both the campaign I'm running and the one I'm playing in are heroic-tier, so I don't know if this will get worse in the higher tiers (it might, given the lack of scaling).