You have some good ideas here, and some I plan to use. I'm just at the just nuts and bolts stage right now... nothing much new in the way of powers or feats till I get familiar with the system. I like:
Freeing up all feats at chargen (expert and adept 4 and warrior 5).
Ability-specific powers: I like the idea of certain powers requiring certain ability mods, though I am considering a few options based on supernatural "traditions" (source from whence powers are recieved)... but my basic adept will use whatever mod the power calls for, for the most part, depending on setting. I definitely don't care for the "choose your own ability" thing for the settings I have in mind.
Your Counter-Magic ideas are sound. I have been toying with an adept tradition that focuses on fast-casting via shouts and songs and specializes in counterspell-type powers and utility, and I think your mechanic there will help flesh that out and gimme some ideas
Mental Finesse: velly velly nice. Definitely needed imo.
Some of my own/others I am thinking of using:
Skill Training: each time you take this feat, add two known skills. The rank for these skills is (character level +3) /2 or expert level, whichever is higher. Alternately, select one skill at character level +3. Increases the expert's skill-based advantage over warrior and adept while overall making gaining skills harder. I like each skill to be something meaningful for characters in my games since so much of the adventures tend to be light on combat and heavy on interaction and skills. Maybe harsh, but playtesting will tell. Maybe straight-up d20 skill points would work better, I dunno.
Parry: modifier is STR/DEX rounded up. Allows for full Str bonus even if Dex is only slightly lower (or vice versa). Balances the logic of parrying and the balance of the mechanic in the game I think. Very minor and possibly inconsequential issue, but it makes me feel better inside.
Weapons have Str requirements. If Str of character is lower than req, subtract the difference from all attack and initiative rolls with that weapon. One-handed weapons may be wielded with 2 hands to lower this penalty by one. (optional: materwork/empowered reduces str req by one?)
Weapon damage bonus is subtracted from initiative roll. Masterwork weapons reduce this penalty by one.
a character may take a number of Wild Talents equal to WIS+1. Normal control loss is applied to these powers. All Corruption checks have a -2 applied to any Wild Power use if it warrants a check. Additional Wild Talents may be taken past this "safe" number, but all Corruption and Fatigue checks for these additional powers suffer a -2 penalty, and a Corruption check is made every time one of them is used, even during loss of control. (if you can't tell I LIKE loss of control!)
Any use of a fatiguing power is subject to an armor check penalty +1 (i.e. the penalty is one worse than it normally would be) if armor is worn while casting.
Strength of Power: allows one's STR to subtract from the armor check penalty applied to fatiguing powers.
About it for now.