Now, I've heard how bad destruction is, primarily because the mana cost to damage ratio is so skewed. My problem with runes is that they have that problem, PLUS the manner in which the player uses them can be awkward. I can only think of two ways to use runes: put it down in front of a charging enemy or use it in an ambush. The former is just not very efficent mana-wise, and the latter just doesn't work because, even with dual casting, it doesn't pack enough of a punch to really do anything.
Ideally, I would want to use runes to set up a sort of mine field into which I could lure enemies. One problem here though: you can only lay down one rune at a time! As far as I'm concerned, the limit makes no sense, getting rid of it would make runes infinitely more useful, and it would still take a butt-load of mana so it couldn't be considered overpowered.
Other ideas? Or does anyone else have any successful strategies they use with runes currently?