Three things: skill powers, mana recovery and balancing powers.
Skill Powers
Some powers are encounter utility powers that can be used with skill checks. Obviously, they're pretty powerful with a mana system, as mana is rarely used outside combat. As part of a simple skill check, it's probably fine to let them be spammed as much as you like. In an extended skill check, it's probably best to allow them to be used only once per encounter. Alternatively, you could make them daily powers and have their bonuses last until the end of the encounter.
Mana Recovery
Here's a way to do mana recovery:
Mana Recovery: you can spend a healing surge but regain no hit points as a standard action or as a free action immediately after using an at-will attack power. If you do, you regain 1 EMP. This increases to 2 EMP at 11th level and 3 EMP at 21st level.
Very conservative, no recouping of DMPs which you can heal with (see below for more on these lines). Gives players a break from spamming at-wills with a pretty high cost.
Balancing Powers
I've noticed this system really puts an emphasis on balancing the quality of powers. With the normal system, it's not too bad if there's a really strong power; you can only use it once anyway. With this system, the strong powers will be used repeatedly and that can break the game.
There's another interesting effect. Clerics, thanks to reusing powers like Consecrated Ground and Mass Cure Light Wounds, can cheaply heal the party after they've run out of healing surges. A party with a Cleric can fight much longer than parties with a different Leader class. I'm wondering if this is a good thing. On one hand, parties lasting through more fights could be a good thing but parties will view the other Leader types unfavorably. This would suggest giving the other Leaders at least one (slightly worse?) power that heals without using healing surges. On the other hand, there might be pressure on the Cleric to save his DMPs to heal the party, which would be a bad thing. This would suggest limiting the healing in some way, although I'm not sure how to accomplish this.
You should probably make any encounter power that regains hit points without spending a healing surge either a daily power (with boosts to damage and a miss effect) or provide temporary hit points instead. It's not desirable if people are drawing out combat so they can heal more with encounter attack powers. The specific powers in the PHB are Inspiring Strike (Cleric 13) and Renewing Strike (Paladin 13).
This brings us to a related problem with Clerics. Cure Light Wounds, Cure Serious Wounds, and Mass Cure Light Wounds are all heroic tier powers and they all cost 1 DMP. Cure Light Wounds is looking like a terrible choice, especially since there aren't any other really awesome utilities at levels 6 and 10. Annoyingly, even if we want to bump up Cure Serious Wounds and Mass Cure Light Wounds, there is only one level of paragon and epic class utility powers each: 16 and 22. I think they could both be level 16 powers, bumping Astral Refuge to 6th and Cloak of Peace to 10th. Alternatively, you bump Cure Serious Wounds only to level 10, and give Cure Light Wounds a perk like only requiring a minor or move action or something.
Some really bad problem powers (I'm sure there are more than just this, but these are the most urgent):
- Stunning powers in general. Again, have some sort of nerf to combat stunlocking.
- Rain of Steel, Unyielding Avalanche, Reaper's Stance (Fighter). Recommend changing it to one basic attack against an adjacent target at the beginning of your turn. Otherwise these WILL be up every combat because they provide an insane DPR boost.
- Blade Cascade. Can you imagine it being used every combat at only 2 DMP? Definitely needs a further nerf. I'm thinking you get 2 primary attacks automatically, and for every primary attack hit you get a secondary attack that only deals 1[W] damage. So, kind of like Rain of Blows. This would also be with the 0th and 2nd multi-attack nerfs in that thread in my sig.
. I just added +1 EMP to every level. The other way I could do it is remove the level 12 (for symmetry) or level 26 (because I don't think those will ever be encounter powers) +1 EMP, and keep the max at 15 EMP. I don't think it really matters.
I took off the level 2 EMP bump. I don't know if anything else needs adjustment, other than giving monsters some form of stun resistance which is a separate issue. What are your thoughts, ameinild? Anyone want to playtest this? 
