"Adjacent" seems to be causing a lot of trouble here. I intended it to mean any card positioned next to the target card--border to border, or overlapping edges (as when partially behind/in front of target.) Any creature card further away would get 1 damage. This would NOT include immaterial/immortal creatures, but
could include burrowed creatures since electricity runs into the ground (I hates me some shriekers/devourers.)
As for the cost, I understand the Delreich's sentiment but am not sure if it stands up to scrutiny. Perhaps upping costs to 4/3 would be fair. But let's compare the 4/2 proposal to other spell cards:
RoF: As originally posted, the new lightning would cost less than RoF (7/5) but RoF hits EVERY targetable creature with 3 damage. Cannot be played directly against opponent. Slight advantage to RoF here.
Fire bolt The new lightning would cost more than fire bolt (3/1) and fire bolt's damage ranges from 3-infinity to single creature and can be played directly against opponent. No clear advantage here.
Rage potion costs less (3/3) and does 5/6 damage to a single creature. Cannot target opponent and no area of effect, so advantage to lightning.
Thunderstorm is cheaper (2/1) and hits every targetable creature with only 1 damage. Cannot be played against opponent. New lightning would be stronger and more versatile, but twice as expensive.
Unstable gas: I'll skip this one since it requires fire and does damage to creatures on both sides AND 20 to opponent.
Side note: I think air needs a new spell,
and am working on an idea already, **see end of paragraph** but thunderstorm is one spell that I feel is clearly weaker than my proposed reworked lightning. Not sure it's fair to put thunderstorm in air to begin with since you're most worried about the lightning and not the thunder anyway....
Twister/Tornado proposal:
http://elementscommunity.org/forum/index.php/topic,2901.0.html 
Drain life costs less (3/1) and does 2-infinity damage and can be played directly against opponent. New lightning would have greater field of effect but as it has capped damage and does not restore life to player, so no decisive winner here either.
Ice bolt is cheaper (3/1) and does 2-infinity damage and can be played directly against opponent. Can also freeze creature. Again, compare with drain life above but with freeze chance instead of restore life--so no clear winner imho.
Gravity pull is cheaper (2/1) and indirectly can "do damage" up to the hp of creature. This nearly always results in destruction of creature, no matter how many hp. Cannot target opponent directly. Maybe an advantage here to lightning, but not for removing dragons/high hp creatures.
Plague costs the same (4/2) and does unlimited creature damage (till death), though only 1/turn. Cannot target opponent. Favor lightning for its instant damage, but for large armies of low hp creatures plague is probably your better spell.
Poison costs less (1/2) and does 2-3 damage/turn to opponent directly. Does not target creatures. Again, you weigh instant vs continued damage: lightning would do max 30 hp damage (if played all 6 cards) vs max 12-18 damage
per turn. There's a reason speed poison decks are so effective. Advantage poison imho.
Chaos seed is cheaper (1) and can do just about any of the above. Hard to compare, but likely advantage lightning for its area of effect and ability to hit opponent directly.
Mutation is cheaper (2) and can kill, create 5/5 abomination or new mutant. Target selection plays a big part in the decision tree here (i.e., you're not likely to play mutation on a photon), but since mutation is totally random, lightning has advantage for definite damage, area of effect and ability to hit opponent directly.
Overall, I don't think 4/2 is too low a cost, but 4/3 wouldn't kill me either. Aether cards have such a high cost to begin with I thought I'd cut aether users a break....
