Very interesting has to look into this
, the alternate cast function will solve many of the issues. I liked the idea of water walking on slaughterfish, that is the fun part of magic try out weird effects.
For an even better control holding down block while charging will charge a secondary parameter like area of effect or duration,
Just a few spells like weakness or frenzy radius, strength and duration, most will do with strength and (radius or duration) the few exceptions could be solved with spells/ effects of different strengths leaving only radius and duration.
I did not like the idea of caps on radius or duration, different spells are used in different ways, I almost always use on target destruction spells would not want to waste effect on area effect here, frenzy, silence and weakness is the only attack spells I use except the "die stupid critter" drain health 100 in 20 feet spell.
Neither did I like the fail if overcharging, many times you will have to wait because the target moved behind cover or moving a way who makes him hard to hit. Spell might fail after a time to avoid people to charge up a spell if they run into an enemy.
However the description of spells in Skyrim does not sound like they are chargeable, press button to cast fireball, hold down to for flamethrower. Cast on ground in front of you for a rune trap. Yes we has only heard about a couple of spells but charging sounds no more plausible than the spellmaker at this point.
http://www.youtube.com/watch?v=cB9g3CRmTok&t=1m42s I believe
Well caps need to eliminate long charging time on some spells for example Novice in destruction have fireball spell,
(http://www.youtube.com/watch?v=bv7WeZmj2G0&t=2m46s then flame bolt-arrow spell and use both hands of caster, fire ball have explode target contact with stagger or thrown and area of effect abilities)
Fireball with starting power 10 and charge up to 30 range of spell 3( R ), cost 25( C ) Apprentice 30 to 70 (R4C50) Journeyman 70 to 120(R5C100) and so on, so Journeyman no need to spend much time to charge spell from novice 10 to journeyman 70 since Journeyman already mastered this level, I think maximum cap of spell can be overcharged (nice to see some changes in FX of spell of charged spell thats will show player Danger of such powers) if %PCname have enough Fatigue and Magicka reserves (fortified by some buff or tactically need now to have more powerful spell right now) since charging will drain Magicka with different rates according to power of spell player can manage their magical reserves for better tactics in combat uncharged fireball will do his minimum caped damage anyways but ability to make double or triple it with charging will be very charming for player
Another thing its will make more difference between barbarian-warrior who found in tomb and wear artifact ring enchanted fortify Magicka 1000 and learn Fire Ball spell from local magic shop and Member of Mage Guild who actually spend half of his life to study magic, warrior can cast thats spell with novice level and use his magical reserves for charge spell more, he feel how such powers drain fatigue from him and see how unstable Fire Ball become in his hand, his hands tremble those heavy iron gauntlets make his fingers moves unagile and slow he need release such devastating powers right now or they will become uncontrollable if he continue to charge spell furtherer fireball ultimately will explode at his face or miscasted in some another way (http://www.tesnexus.com/downloads/file.php?id=25844 has many examples so there can be not only Morrowind like fizzle) so he decide cast it right now at target, fire ball do 99 damage, Magicka draining cost was 380, around he spend more of his fatigue at cast then skillful mage but he is Warrior and have high Endurance attributes so Fatigue it not problem for him, but also he spend more time at casting of spell since he need to form fireball and charge it from 10 to 99
And now we take example of skillful Apprentice of Mage Guild, he wear light spider silk gloves enchanted to enhance his magic skills in destruction enough to reach journeyman level he has mage guild training thats enhance his Will attribute so have enough Fatigue to try cast Fire Ball spell, he try thats many times and know how feel thats powers in hands so he also decide to charge his fire ball spell more besides he curios about thats new enchanted gloves and want to know how much more powerful they make him, he start at journeyman level of fire ball so if he cast it right now after forming it up minimum cap of damage already be at 70 he use his Magicka reserves to charge spell more, since there is no thing thats will his hands unagile (or even thats an elf or khajiit girl who more agile then bulky nord warrior) Apprentice can charge spell furtherer more and eventually release charged fire ball damage was 110 since spell was charged at journeyman level and cost 280 since our mage have Apprentice training in Destruction.
But wait our mage has some nice perks what he discover during of study of destruction magic like
Ignite
perk thats add damage overtime to all fire element spells,
Searing flames perk
add weakness to fire to fire based spells
Burning pain
Burning enemy stagger in pain more frequently, destruction magic can bring pain in life not only to enemies but for caster also study this allow mage found ways bring more Pain to enemies
So they can also be applied to casted spell as additional side effects
Thats situation fit to lore very well since in TES different organizations thats provide special training and have special facilities like Battlespire for battlemages and spellswords or Arcane University and local mage guilds for mages of different schools, there also other organizations thats can train skills, cell spells and magic items, provide some arcane services.
Organizations like temples (thats can train restoration, cure disease) or covens of witches, don't forget about Daedra Worshipers and Necromancers also, they all can provide quests, services, train skills and teach spells.
So battle mages actually can have special training thats will decrease penalties for casting in armors but also can provide unique perks like channeling spells into weapons without enchanting.