I seem to be in the minority, but I loved the Symbol of Insanity tactic used by Xykon, and I'd let a PC use it in my game. It's clever, stylish, and extremely effective. Balderdash to what the SRD says; the DM is allowed to use DM fiat to allow or to do extremely cool things like bouncing balls with symbols of insanity.
I think this was a good strip for several reasons already mentioned here. And while I do not discourage discussion of the mechanics of OotS, I believe it is a web comic first, and then a D&D simulation second, and thus stuff you guys are calling "lame" is perfectly fine with me.
That, and this strip was mildly disturbing, which is sort of unusual for the strip. Usually it is disturbing in a funny way. There was nothing funny about this strip, it just showed off how badass Xykon is, and that a room full of paladins is no match for an uber-level lich.