There are quite a few obvious power game builds for destruction but from what I can tell very few, if any, make use of runes. While leveling destruction, grinding my DiD legendary character towards level 81, I found them extremely efficient for gaining levels, but that's not all.

I've taken rune master, a trait I never though even remotely valuable before, and I'm finding I've reached a very effective combat style/strategy strangely reminiscent of my absurdly overpowered Oblivion mage character using runes. Granted I'm using 100% destruction reduction enchants since I would never bother w/destruction w/out them, and runes without it would be too expensive to bother with.

Using a storm atronach(immune to its damage) or two to gather enemies up and spam lightning runes, of course with the +shock damage in destruction, has been surprisingly effective and absolutely chews through everything - and keep in mind legendary enemies take 1/4th damage from the player. I'm wondering if there's something off/bugged with the spell since it seems to kill even a single enemy faster than thunderbolts (which do 50 damage vs. the rune's 60). I'm dual casting them of course as well. I can't figure out exactly why they seem so effective though, or if I'm just somehow misjudging something. Perhaps it's their ease of use/quickly spam-able nature compared to the somewhat more aim-requiring thunderbolt, but I doubt it. I'll have to test it with some console commands eventually.

Then I've also noticed that, at least indoors where sneak seems to be far more effective, I can often spam them on enemies from stealth(with quiet casting perk in illusion of course) without them finding me. Which is basically how my mage worked in Oblivion with invisibility combined into my damage spells in very short duration. Rune master of course makes it especially effective for this, allowing me to rain runes down on enemies from a greater distance while remaining in stealth as I do so.

Ease of use, range, damage, and of course effectiveness from stealth all seem to favor it over thunderbolt spam except perhaps against single enemies you want to impact stagger-lock. And of course, against flying enemies like dragons it's not so great until they land. Anyway, I've been finding it way more effective than I expected and am considering going for destruction as my damage source over archery.

As for lightning rune vs. fire or frost there are mutliple points -

1. Fewer enemies are resistant to shock

2. Shock spells other than the rune are the easiest to hit enemies with due to much shorter travel time on ranged spells when you want to use them

3. Shock has the best/only worthwhile master spell, Lightning Storm is actually decent for melting large enemies and laser beaming dragons in flight

4. The strongest/most useful atronach is probably the storm atronach so it's best to pick what it's immune to

Fire might be worth considering just due to its extra burning damage, but really I doubt it'd add up to that much more damage considering how quickly things go down when you rune spam them.

Finally. Someone who realizes the power of the Destruction school in Skyrim, lol.

Another fun little sneak thing you can try out, if you have Dragonborn. Get some oil spiders and summon one, let it get 'found' and have it fight while you are in hiding... If it dies, who cares. That one is specifically to get the oil on the ground. Place a fire rune somewhere within the oil then get out a few more oil spiders while finally alerting the enemy to you. If at the right spot, the spiders will meet the enemy at the fire rune and if oil spiders die by fire... Well. Have fun watching the show.

~Edit~

Oops. Forgot to mention. Place a Paralyze rune as well to paralyze the target right in the middle of all that lovely show.

The higher damage (and the cost) is probably there due to the fact that devs likely intended the spell to be cast once as a trap instead of being spammed on enemies in the middle of the combat.

I'm not sure it's not used as much as you think, destruction skill increases based on the damage, and given the high damage and great availability of the spell I'm sure tons of people, myself included, use it for both combat and great destruction training. I even often use it in the exact same manner- combined with the atronachs.

Well back when I was last active on the forums it was all about using impact, which runes don't benefit from.

I also think it's doing higher damage than the in game info suggests, or perhaps it gets a bigger benefit from dual casting. I googled around and one player did suspect that it did more damage the closer to the center of the rune enemies are when it explodes on them, which would explain why casting them on top of enemies is so effective if that's true.

I've honestly started using a lot of Lightning Runes myself as well. Kind of weird.

edit - i've never tried it dual casting, will have to get that perk soon to see how it works. I'm really trying to focus on making a "pure mage" build with this character, so it will be interesting to do something different.

Runes are fun to use, in my opinion. As mentioned that are a good way to level the destruction skill too. They don't work too well when you have a follower with you though, if you know what I mean.

I've never used followers personally so no worries there. However, putting magic/shock resist gear on a follower would prevent most of the damage wouldn't it?

My follower is immune to magical damage actually and apparently he can't set mine off. Then again, I hadn't used runes much close to him. (He normally stays out of the way).

After testing with getavinfo health, looks like dual cast runes are doing ~3.3x normal damage rather than the 2.2x damage most dual cast spells do. Weird.

Apparently, from what I've been reading, most followers do not actually set them off. However, if an enemy triggers one and your follower happens to be in range of the explosion, they can be hurt by them. Also, assuming the http://www.uesp.net/wiki/Skyrim:Lightning_Rune is correct, certain quest related followers can still activate runes that you set though.

Yep, followers don't set em off, at least no follower I ever used. Magical resistance doesn't matter in this situation because spamming the runes that keep hurting your follower, no matter how small the damage is done to them, will count as hitting them and will eventually make them hostile towards us. Had that happening to me more than I can count, relying on my follower to be out of range.